Dark Chocolate Mousse Cake

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.
  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!!

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 recipe 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
  • Cook Time: 25 minutes
  • Total Time: 5 hours, 55 minutes
  • Yield: serves 10-12
  • 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

  • 1 and 3/4 cups (220g) all-purpose flour (spoon & leveled)
  • 3/4 cup (65g) 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.
  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 here for more information. 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

 

473 Comments

  1. Hi Sally,
    First, I love every recipe of yours that I have tried (and I have tried quite a few lately!). I want to make this cake for my birthday but have a couple of questions. I was planning on cutting the recipe in half and making this as a 6 inch cake but I only have one 6 inch springform pan to work with. How many layers would half a recipe make? Can I make just 2 layers (one at a time) from a half recipe or a single thicker layer and cut it in half? Can I put a single thick layer of mousse between them? Would the mousse hold up to that without the gelatin for structure (I’m OK adding gelatin if needed but how much)? I do love chocolate (and coffee) so I would use dark and bittersweet all the way. This is a chocolate lovers dream cake.

    1. Hi Shelly! I’m happy to answer your questions. (1) I’m unsure exactly how many 6 inch cake layers half of this recipe would make, but my guess is 3 layers. (2) Using half the recipe, there is definitely too much batter for 2 6 inch cakes. They would be too thick and I can’t see them baking very evenly. (3) No need for gelatin in the chocolate mousse.

  2. I have made your chocolate moose cake . It was a hit. Can I make the cake into cupcakes ? I don’t want to use the moose . I also make some ahead of time and freeze them . What a life saver . Love your recipes . Thank you

    1. Hilari @ Sally's Baking Addiction says:

      Hi Ellen, See the section in the post above called “What About Cupcakes?” So happy you’ve been enjoying our recipes!

  3. Hey Sally! Giving this cake a try for the first time. Will this cake with its mousse filling be stable enough for a fondant covering?

    1. Stephanie @ Sally's Baking Addiction says:

      Fondant shouldn’t be a problem, Saman.

  4. Planning to bake this for a bday party. But I ordered the wrong pan sizes…ughh. I now have two 9inch and two 8 inch pans. Can I bake this in two 9 inch pans and cut into layers?

    1. Stephanie @ Sally's Baking Addiction says:

      Hi Neha, It’s too much batter to only use 2 pans. Instead, bake the first two layers and keep the remaining batter covered at room temperature while the first 2 layers bake. Hope you enjoy it!

  5. Baishali Chaudhury says:

    Hi Sally
    I have made this cake and its awsome i wanted to know if i can make it as a sheet cake. How many cups of batter is this recipie. And how do i modify for a 9×13 inch cake

    1. Stephanie @ Sally's Baking Addiction says:

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

  6. Can I make it 24 hours before and serve at room temperature the next day?

    1. Stephanie @ Sally's Baking Addiction says:

      Hi Katie, If making this cake the day before serving, you can place the entire cake in the refrigerator and then take it out an hour or two before serving to bring it back to room temperature.

  7. Question. I wanna bare this cake for my best friends bachelorette party but I only have 2×30 cm pans.. can I just bake it in two of these and then cut it in half to make a 4 layers cake?

    Best regards Betina

    BEST

    1. Stephanie @ Sally's Baking Addiction says:

      Hi Betina, You can use this post Cake Pan Sizes & Conversions to help calculate how much batter you would need for different size pans. Happy baking!

  8. Can I add strawberries throughout the layers or is there to much liquid in the strawberries?

    1. Stephanie @ Sally's Baking Addiction says:

      Hi Kate, We recommend only using berries on top. The mousse may liquefy a bit with sliced strawberries inside.

  9. Hi Sally,

    I’m hoping to make this cake for my dad’s birthday which is coming up. I was hoping to do like a drip thing on top with the ganache instead of covering the whole cake, so I’m wondering if the chocolate mousse would work for frosting the whole cake instead of just a filling/crumb coat ? Thank you!

    1. Stephanie @ Sally's Baking Addiction says:

      Yes, that would work. This cake looks beautiful with the ganache as a drip. Enjoy!

  10. This is the Best chocolate cake I’ve ever had! I can’t believe I’ve been making boxed mixes all this time! Your directions are easy to follow & I like how you separate the steps. I was introduced to your website by our favorite Disney YouTubers Tim & Jenn Tracker, they’ve featured several of your recipes on their vlogs! We also tried your banana bread recipe at their suggestion, and again, why did I use box mixes! Next on the list brownies! Thank you for sharing!

  11. Can I substitute cake flour?

    1. Stephanie @ Sally's Baking Addiction says:

      Hi Kristin, We don’t recommend it. Chocolate cakes already have cocoa powder— which is a VERY fine dry ingredient. The combination of cake flour and cocoa powder usually results in a flimsy cake.

  12. This is literally my favorite cake! I have made it for all my kids birthdays this year. I make the cake exactly as directed and then make sallys buttercream to decorate! We made an Elmo cake, a ninja turtle cake, and today a rodeo cake. The ganache is such a nice base to decorate on top of and with the buttercream on top it’s such a nice contrast of flavors. I only make 3 layers tho which seems to be perfect. Wish I could include pics! Thanks sally you have given me an excellent recipe and confidence to make homemade cakes for my kids

  13. Hi Sally. I made this cake today and the cake part itself is fab! However, I stumbled at the mousse. When I added the water/cocoa powder mix to my melted chocolate it turned to cement. Any idea what went wrong? Thanks a lot.

    1. Hi Jamie-Lee, are you using pure chocolate baking bars? I recommend Ghirardelli or Baker’s brands. And don’t discard what you have! You can warm it back up/thin it out in a double boiler over low heat. Stir until it comes together. I hope this helps!

  14. This cake was an absolute hit with my family, thank you for the great recipe! Can I use the chocolate mousse made in the recipe to pipe decorate the outside of this cake on top of the ganache?

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