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This super moist dark chocolate mousse cake combines unsweetened natural cocoa powder and dark cocoa powder for an extra rich flavor. Fill the cake with a simplified chocolate mousse and cover the whole dessert with semi-sweet chocolate ganache. If needed, you can prepare the ganache and mousse ahead of time.

slice of dark chocolate mousse cake on a cake server

My s’mores chocolate mousse inspired me to play around in the kitchen the other week. I’ve always loved chocolate mousse, back to my childhood when my mom served it as an easy (yet totally elegant) dessert on the holiday table. Chocolate mousse is simple divinity in its own right, but when paired with chocolate cake, it’s downright decadent.

I made this chocolate mousse cake for my husband Kevin’s birthday. This cake basically demands a huge gathering because– trust me– you don’t want to be left alone with its temptation. It WILL call out your name each time you open the refrigerator.

Taunting you.

chocolate layer cake on a wooden cake stand

3 Parts to Dark Chocolate Mousse Cake

Let’s break down each component of this intensely rich cake:

  1. Dark Chocolate Cake: This is actually a variation of my tuxedo cake, which originated from my chocolate cake recipe. In recent years, I’ve found that replacing sour cream for some of the buttermilk gives the cake more structure.
  2. Chocolate Mousse: I researched simplified ways to make a fluffy chocolate mousse filling without the use of eggs or gelatin. This chocolate mousse filling combines real chocolate and homemade whipped cream. Or our whipped frosting would make a wonderful alternative filling if you don’t want to make the chocolate mousse!
  3. Chocolate Ganache: Top the whole cake with 2 ingredient semi-sweet chocolate ganache. You should be a chocolate ganache pro by now!

Video Tutorial: Chocolate Mousse Cake

Stick-to-the-back-of-your-fork moist. This is every chocolate lover’s dream!

4 layer chocolate cake

Dark Chocolate Cake

Use this chocolate cake as the starting point. For a sturdier, yet moister crumb, swap some sour cream in for the buttermilk and reduce the hot liquid. The acidity in both sour cream and buttermilk is a must to properly leaven this cake. (If desired, see baking powder vs baking soda for more information.) This cake has a natural dark chocolate taste, but to deepen that flavor, use a mix of natural cocoa and Hershey’s Special Dark cocoa powder. A touch of espresso powder and hot coffee further enhances the chocolate flavor. The cake will not taste like coffee– rather, the two add depth to the cake’s chocolate flavor.

  • Why hot liquid? The hot liquid encourages the cocoa powder to bloom and dissolve. If you don’t drink coffee, you can use hot water.

You have options! You can make this cake into 2, 3, or 4 layers. I highly recommend 3 or 4 layers because there’s over 4 cups of chocolate mousse to spread inside. You can use 8 inch or 9 inch pans. The bake times are similar, see recipe notes.

A cup of chocolate chips adds even more chocolate flavor. I used 1 cup (180g) of mini semi-sweet chocolate chips in this pictured cake, but left them out in the video. They’re optional– but definitely worth the addition!!

You can also see this exact cake batter baked as three layers in my chocolate peanut butter cake (try that one next!).

chocolate cake batter in glass bowl

Simplified Chocolate Mousse

The chocolate mousse adds a creamy and light contrast to the dark chocolate layers. You need 6 ingredients:

  1. Hot Water
  2. Cocoa Powdernatural or dutch-process
  3. Melted Chocolateuse two 4-ounce chocolate baking bars found in the baking aisle
  4. Heavy Cream
  5. Confectioners’ Sugar
  6. Vanilla Extract

Whisk the hot water and cocoa powder together. Pour into melted chocolate. The hot water breaks up the chocolate, adding to the airy mousse consistency. Cocoa powder creates additional chocolate flavor. Fold this chocolate mixture into whipped cream– a combination of heavy cream, confectioners’ sugar, and vanilla extract.

2 images of making chocolate mousse including whipped cream and chocolate mixture in glass bowls

Whipped cream + our chocolate mixture. ↑

Fold them together to make our chocolate mousse filling. ↓

chocolate mousse for chocolate cake in glass bowl and between cake layers

Baker’s Tip: The chocolate mousse must chill in the refrigerator before using, so it’s a good idea to make it ahead of time or as the chocolate cake layers are cooling. The mousse is best cold, so I actually recommend serving the cake cold. (Additionally, the cake is much easier to assemble if the mousse is cold!)

2 images of chocolate ganache in glass bowl and pouring on chocolate cake

Chocolate Ganache

I won’t go into a lot of detail about the chocolate ganache because I have a complete chocolate ganache tutorial for you! Like the chocolate mousse, it’s imperative to use pure chocolate. Wait about 20 minutes for the ganache to thicken before pouring onto the cake.

How to Assemble & Decorate Chocolate Mousse Cake

Chocolate ganache enrobes 4 cake layers and 3 mousse layers. Place bottom cake layer on your cake stand or serving plate. Using a large icing spatula, evenly cover the top with about 1.5 cups of chilled chocolate mousse. Top with 2nd cake layer and another 1.5 cups of mousse. Top with the third cake layer, then spread another 1.5 cups mousse evenly on top. (Save a large spoonful of mousse for a thin crumb coat.) Top with final 4th cake layer. Spread any remaining mousse around the sides as a crumb coat. Run a bench scraper around the cake to smooth it out. Refrigerate cake for at least 1 hour and up to 4 hours. Chocolate mousse is pretty fluffy, so the cake won’t hold its shape unless it’s properly chilled.

Pour ganache on top then run a bench scraper around the sides to smooth it out. You can serve the cake immediately or wait for the chocolate ganache to set. 🙂

top of chocolate mousse cake with berries and chocolate shavings
slice of chocolate mousse cake on a white plate

What About Cupcakes?

Instead of a big cake, you can make chocolate mousse cupcakes. Use my chocolate cupcakes recipe and halve the chocolate mousse and chocolate ganache recipes below. Fill the cupcakes with chocolate mousse using my Sugar Plum Fairy Cupcakes as an example. Drizzle cooled cupcakes with ganache. Eat your heart out!

More Indulgent Chocolate Desserts

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4 layer chocolate cake

Dark Chocolate Mousse Cake

  • Author: Sally
  • Prep Time: 2 hours, 30 minutes (includes chilling)
  • Cook Time: 25 minutes
  • Total Time: 5 hours, 55 minutes (includes cooling)
  • Yield: serves 12 1x
  • Category: Cake
  • Method: Baking
  • Cuisine: American

Description

This super moist dark chocolate cake combines unsweetened natural cocoa powder and dark cocoa powder for an extra rich flavor. Fill the cake with a simplified chocolate mousse and cover it with semi-sweet chocolate ganache. If needed, you can prepare the ganache and mousse ahead of time. See notes.


Ingredients

Scale
  • 1 and 3/4 cups (219g) all-purpose flour (spoon & leveled)
  • 3/4 cup (62g) unsweetened natural cocoa powder* (see note)
  • 1 and 3/4 cups (350g) granulated sugar
  • 2 teaspoons baking soda
  • 1 teaspoon baking powder
  • 1 teaspoon salt
  • 2 teaspoons espresso powder (optional)*
  • 1/2 cup (120ml) canola or vegetable oil
  • 2 large eggs, at room temperature
  • 3/4 cup (180g) full fat sour cream, at room temperature
  • 1/2 cup (120ml) buttermilk, at room temperature*
  • 2 teaspoons pure vanilla extract
  • 1/2 cup (120ml) hot water or coffee*
  • optional: 1 cup (180g) mini or regular semi-sweet chocolate chips
  • optional garnish: fresh berries and/or chocolate shavings

Chocolate Mousse

  • 1/2 cup (120ml) hot water
  • 1/4 cup (22g) unsweetened cocoa powder* (see note)
  • two 4-ounce quality semi-sweet chocolate bars (113g each), finely chopped*
  • 2 cups (480ml) heavy cream or heavy whipping cream
  • 2 Tablespoons (15g) confectioners’ sugar
  • 1/2 teaspoon pure vanilla extract

Chocolate Ganache

  • two 4-ounce quality semi-sweet chocolate bars (113g each), finely chopped*
  • 1 cup (240ml) heavy cream or heavy whipping cream

Instructions

  1. Preheat oven to 350°F (177°C). Grease four 8-inch or 9-inch cake pans, line with parchment paper, then grease the parchment paper. Parchment paper helps the cakes seamlessly release from the pans.
  2. Make the cake: Whisk the flour, cocoa powder, sugar, baking soda, baking powder, salt, and espresso powder (if using) together in a large bowl. Set aside. Using a handheld or stand mixer fitted with a whisk attachment (or you can use a whisk) mix the oil, eggs, and sour cream together on medium-high speed until combined. Add the buttermilk and vanilla and mix until combined. Pour the wet ingredients into the dry ingredients, add the hot water/coffee, and whisk or beat on low speed until the batter is completely combined. Fold in the chocolate chips, if using.
  3. Divide batter evenly between 4 pans. Bake for 19-23 minutes. Baking times vary, so keep an eye on yours. The cakes are done when a toothpick inserted in the center comes out clean.
  4. Remove the cakes from the oven and set on a wire rack. Allow to cool completely in the pan. The cakes may slightly sink in the middle as they cool—that’s expected.
  5. As the cakes cool, prepare the chocolate mousse so it can chill and be ready at the same time as the cake layers. You can also prepare the mousse 1-2 days ahead of time. Whisk the hot water and cocoa powder together. Set aside. Melt the chopped chocolate bars in a double boiler or use the microwave. If using the microwave: place the chopped chocolate in a medium heat-proof bowl. Melt in 20 second increments in the microwave, stirring after each increment until completely melted and smooth. Pour hot water/cocoa mixture into melted chocolate and stir until thick and smooth. Set aside. Using a hand mixer or a stand mixer fitted with a whisk attachment, whip the heavy cream, confectioners’ sugar, and vanilla extract together on medium-high speed until medium peaks form, about 3-4 minutes. Medium peaks are between soft/loose peaks and stiff peaks. Pour in the chocolate mixture and using a spoon or rubber spatula, gently fold together. Avoid over-mixing which can deflate/thin out the mousse. Cover mousse and chill in the refrigerator for at least 2 hours and up to 2 days. Makes about 4.5 cups chocolate mousse.
  6. Assemble layers before preparing chocolate ganache: First, level the cakes if needed: using a large serrated knife, slice a thin layer off the tops of the cakes to create a flat surface. Discard (or crumble over ice cream!). Place 1 cake layer on your cake stand or serving plate. Using a large icing spatula, evenly cover the top with about 1.5 cups chocolate mousse. Top with 2nd layer and evenly cover the top with 1.5 cups chocolate mousse. Top with the third cake layer, then spread another 1.5 cups mousse evenly on top. Save a large spoonful of mousse for a thin crumb coat. Top with final 4th cake layer. Spread any remaining mousse around the sides as a crumb coat. Run a bench scraper around the cake to smooth out crumb coat. Refrigerate cake for at least 1 hour and up to 4 hours. Prepare the ganache as you wait.
  7. Chocolate Ganache: Place chopped chocolate in a medium heat-proof bowl. Heat the cream in a small saucepan over medium heat until it begins to gently simmer. (Do not let it come to a rapid boil– that’s too hot!) Pour over chocolate, then let it sit for 2-3 minutes to gently soften the chocolate. With a metal spoon or small rubber spatula, very slowly stir until chocolate has melted and mixture is smooth. The finer you chopped the chocolate, the quicker it will melt with the cream. If it’s not melting, do not microwave it. If needed, see Troubleshooting Chocolate Ganache. Once ganache mixture is smooth, let it cool for 20 minutes at room temperature before spreading on chilled cake.
  8. Pour/spoon ganache on chilled cake. Smooth the top with an icing spatula and the sides with a bench scraper. Top with optional garnish such as fresh berries and/or chocolate shavings. Serve cake immediately or chill, uncovered, for up to 4-6 hours before serving. Cake can be served at room temperature or chilled.
  9. Cover leftover cake tightly and store in the refrigerator for 5 days.

Notes

  1. Make Ahead & Freezing Instructions: Prepare cake through step 4. Wrap the individual baked and cooled cake layers tightly and refrigerate for up to 2 days or freeze up to 3 months. Bring to room temperature, make mousse filling, then continue with step 6. You can prepare the chocolate mousse in advance. See step 5. You can also prepare the chocolate ganache ahead of time too. Refrigerate prepared ganache for up to 2-3 days. Bring to room temperature before spreading onto cake. Frosted cake freezes well, up to 3 months. Thaw overnight in the refrigerator, then bring to room temperature or serve cold.
  2. 3 Layer Cake: You can also prepare this cake as a 3 layer cake. Divide batter between three 8-inch or 9-inch cake pans and bake for 22-25 minutes or until a toothpick inserted in the center comes out clean. Use about 2 cups of chocolate mousse between each layer.
  3. Espresso Powder/Coffee: Espresso powder and coffee will not make the cake taste like coffee. Rather, they deepen the chocolate flavor. I highly recommend them both. If coffee isn’t your thing, you can leave out the espresso powder and use extra hot water instead of the hot coffee.
  4. Cocoa Powder: For the best dark chocolate flavor in the cake, I recommend using a blend of unsweetened natural cocoa powder (1/4 cup; 22g) and Hershey’s “Special Dark” cocoa powder (1/2 cup; 43g). Hershey’s Special Dark is actually a mix of natural cocoa powder (an acid) and dutch-process cocoa powder (a base) and it worked fine in this recipe. This recipe needs acidic natural cocoa powder, so do not use ALL dutch-process cocoa powder. For best results, use 3/4 cup (65g) natural or the blend of natural/Special Dark I used. For the chocolate mousse, you can use either unsweetened natural or dutch-process cocoa powder. (Or the Hershey’s Special Dark.)
  5. Why Room Temperature? All refrigerated items should be at room temperature so the batter mixes together easily and evenly. Read more about why room temperature ingredients are important. Instead of sour cream, you can use plain yogurt. The cake won’t taste as rich, but it’s a fine substitute.
  6. Buttermilk: Buttermilk is required for this recipe. You can make your own DIY version of buttermilk if needed. Add 1 teaspoon of white vinegar or lemon juice to a liquid measuring cup. Then add enough whole milk to the same measuring cup until it reaches 1/2 cup. (In a pinch, lower fat or nondairy milks work for this soured milk, but the cake won’t taste as moist or rich.) Stir it around and let sit for 5 minutes. The homemade “buttermilk” will be somewhat curdled and ready to use in the recipe.
  7. Chocolate in Mousse & Ganache: Mousse & ganache will only set if the correct chocolate is used. You can use high quality chocolate chips if needed (I prefer Ghirardelli semi-sweet chocolate chips), but I recommend using pure chocolate baking bars. You can find them right next to the chocolate chips in the baking aisle. They are sold in 4 ounce bars. I like Bakers or Ghirardelli brands.

Keywords: cake, chocolate mousse, dark chocolate

Reader Questions and Reviews

  1. Hi Sally! Can I design the cake and add the mousse and ganache one day before serving?

    1. Hi Sally, all the make-ahead instructions are included in the Notes section of the recipe card. Hope you enjoy the cake!

  2. Can the stacked cake be stored in the freezer before pouring the chocolate on top?

    1. Hi Ilana, see recipe notes for our recommended freezing instructions!

  3. Hi,

    If I use this recipe to make cupcakes, do I still need to only fill the cupcake liners half way full as described in the Moist Chocolate cupcake recipe?

    Thanks!

    1. Hi Nav, yes, we recommend only filling the liners half way. Enjoy!

  4. This is an amazing cake. The mousse and ganache are not overly sweet and were a big success with my buttercream hating household!

  5. I am so excited to try this. I have two questions – Would you recommend substituting the semi-sweet baking bars in the mousse and ganache for 60% baking bars (or even higher)? The darker, the better for me, but I do not want to mess with the integrity of either if not recommended. My second question is regarding the sour cream – I love the stuff, but my husband hates it, and somehow can detect it in ANYTHING. Could whole milk ricotta work as a substitute? Thanks in advance!

    1. Hi Britt, you can use darker chocolate bars for a dark chocolate mousse and ganache — same amount. Instead of the sour cream, plain full fat yogurt or Greek yogurt would be your best substitute. Hope you enjoy the cake!

  6. Hii Mrs Sally….
    Me & my daughter so excited to make this recipe
    But I have a problem….
    I can’t find buttermilk…I just have dry buttermilk…
    can I use dry buttermilk? & How many gr?
    And how about consistently the cake? Should I add a milk ? Or water?
    Thank you for the answer….stay safe & healthy always Mrs Sally

    1. Hi Eni, dry buttermilk should work just fine in this recipe. Follow the directions on the box of dry buttermilk to make the 1/2 cup (120ml) buttermilk needed for this recipe. Hope you and your daughter enjoy the cake!

      1. Hi!
        1) Do I HAVE to wait for the cakes to completely cool before taking them out of the cake pans? I’m making two of these

        2) I’ll be assembling the cakes tomorow, do you suggest I freeze them or refrigerate for the evening?

      2. Hi Samantha, you can refrigerate them. All the make-ahead instructions are included in the Notes section of the recipe card. Hope you enjoy the cake!

  7. Hi Sally, my nephew asked me to make a chocolate mousse cake for his birthday, of course I said yes. I have never made a chocolate mousse cake before. Then I came across your Dark chocolate mousse cake recipe and it was absolutely delicious! I took a piece to make friend to taste and she asked if I could make it for her next birthday.

  8. Hi Sally! I only have 1 cake tin at home.. do you think I could pour all the batter into the 1 tin and split it in half after it cools, or is this going to end up a crumbled disaster? Thank you!

    1. Hi Emily, we don’t recommend baking it all in one cake pan, as it could overflow and bake unevenly. Rather, you can bake the layers one at a time, leaving the leftover batter covered with a clean towel at room temperature while waiting for the current layer to bake. Hope you enjoy the cake!

  9. I’ve done this recipe before but with cupcakes but I cant remember how long to cook them for. I thought I saw it in the comments. it said how full to fill them and how long.

    1. Hi Nicole, you sure can make these as cupcakes! See section titled “What about cupcakes?” for more details.

    2. Can this cake be made in a 13 x9 x 2 glass pan and is it enough to make 2 at this size?

  10. Wow,was this delicious! The many steps were worth it. My taste testers felt that the cake needed a deeper chocolate flavor with more moist texture,but overall a very luxurious taste.

  11. I first made this cake back in July for my wife’s birthday. She loved it so much, she immediately recommended it for a friend’s upcoming birthday celebration. As I prepare to make this cake for a second time, I wanted to reach out with a word of thanks. This cake recipe is absolutely delightful, a fun and manageable project delivers exactly as promised. It haunts, it makes you ruminate and drives to distraction. So much fun, Cheers!

  12. By far the best homemade chocolate cake I’ve ever made. I made this for my Mom’s birthday this weekend and it was a huge hit. Moist, deep chocolate flavor throughout and the mouse and ganache – perfection! I will definitely make this again.

  13. By far the best homemade chocolate cake I’ve ever made. I made this for my Mom’s birthday this weekend and it was a huge hit. Moist, deep chocolate flavor throughout and the mousse and ganache – perfection! I will definitely make this again.

  14. Hi Sally,
    I really liked your very simple Ganache and Mousse recipe. I made the mousse but while mixing the cocoa + chocolate and whipped cream, I deflated the cream. Is there any way to salvage it? Can I whip it again after refrigerating for a couple of hours??
    Thank you

    1. Hi Bhavi! The most common cause of a thin mousse is over mixing. If you try it again, avoid over-mixing which can deflate/thin out the mousse. And also, make sure you chill it in the refrigerator for at least 2 hours before using. Unfortunately, there’s no great way to re-whip it once combined.

      1. Thank you Sally. I think I mixed the chocolate mixture with the whipped cream while it was still warm. Anyway I’ll try to see how it turns out. I need the cake tonight so may not be able to wait for another batch after 2 hours! Hoping for the best! Thank you for the reply!

  15. Hi Sally. The chocolate mousse looks divine. Can the mousse be used as a frosting on its own for another cake I’m baking? Will it hold its shape if the cake is cold?

    1. Hi Panjami, You can use the mousse to fill and frost a cake, just like we do here before the ganache is added. You won’t be able to pipe it but it should be fine to cover a chilled cake.

  16. Regarding the conversion to Cupcakes. Do I have the actually HALVE the QUANTITIES in both recipes you suggested then mix them together to make the Mousse Cupcakes ???

    1. Hi Dale, you can make cupcakes using this cake batter rather than the chocolate cupcakes, and use the full amounts of mousse and ganache. You simply will have a larger yield of cupcakes.

    1. Hi Mary, You can bake this cake in a 9×13 inch baking pan. Same oven temperature, about 35-40 minutes bake time.

    1. Hi Sara! We haven’t tested a mocha mousse recipe. You start with adding extra espresso powder – let us know if you give it a try!

  17. I make this cake for my brother’s birthday every year because he loves it so much! The only thing is, we don’t like the chocolate ganache on top. It’s too thick and takes away from the fluffyness of the mousse and cake. Instead I double the mousse and it comes out amazing.

  18. Hi, can I use self raising flour instead of all purpose flour is i leave out the baking powder/baking soda?

    1. Hi Emma, we don’t recommend it. Self-raising flour isn’t always a 1:1 swap with the all-purpose flour + rising agents, so it would take some recipe testing to determine the proper swap. Best to stick with all purpose flour here.

  19. This recipe is off the charts awesome and made it for my husband’s birthday! I am making it now for my son’s birthday but want to frost with buttercream frosting. Is that ok? Should I do the crumb layer with buttercream and not mousse?

    1. Hi Meg, yes, you can use buttercream here instead. We still recommend a crumb coat — with buttercream will work just fine!

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