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.

dark chocolate mousse cake

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

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

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.

making chocolate mousse

Whipped cream + our chocolate mixture. ↑

Fold them together to make our chocolate mousse filling. ↓

chocolate mousse for chocolate cake

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!)

chocolate ganache 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

chocolate mousse cake

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. If needed, you can use whole milk mixed with 1/2 teaspoon of white vinegar or fresh lemon juice instead of buttermilk.
  6. 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

 

150 Comments

  1. I want to make this cake at home, then take in the car to a family gathering that is a 3-hour drive away. Is it OK to transport out of the refrigerator for that long? My cake holder would not fit in our cooler.

    1. That time out of the refrigerator would be just fine, but for best taste, I recommend chilling in the refrigerator for at least 1 hour when you arrive and prior to serving.

  2. Hi Sally,
    I’m worried about my mousse. When I combined the water/cocoa mixture with the melted chocolate, it became quite stodgy. Think of soft Play-Doh…not quite solid, but certainly not something I can “pour” into the whipped cream, as instructed to do.

    If I try folding it into the mousse, I think it’ll be a massacre. Is there anything I can do?

    1. Hi Jacquelyn, The chocolate mixture will be fairly thick but they will still fold together. You an see that mine isn’t a thin liquid in the photo above where I show the bowl of the whipped cream next to the bowl of the chocolate!

  3. ❤️❤️❤️❤️❤️❤️ Love chocolate so much so this made my day! Will totally make again and again and again and again!!!! ❤️❤️

  4. Absolutely delicious! Dark, rich, decadent cake. I didn’t find the dark cocoa so used all regular and still so good with a deep chocolate flavor. Thanks for an amazing recipe!

  5. Hi Sally. I made just the cake layers so I could use up some ingredients and to freeze so I can’t comment on the taste yet but I did run into a problem. Up above you suggested to Danielle to use 2 9in pans. That’s what I did because I only have those. I made the batter (which was I think thee easiest one I’ve ever made from your recipes, lol) and it came out exactly like yours. I divided it between both pans and baked for the time you suggested in that comment as well as keeping my eyes on them. But sadly my cakes sunk in the middle. I know using expired baking soda/powder and putting too much batter can cause this to happen. As for mixing. I made sure not to over mix as well. I know it wasn’t my baking soda/powder because I had just used them both to make a cake the day before. The only thing I can think of as to why it happened was over filling the pans. Just wanted to get your take on this because I do plan to make them again. And if it was due to that I just wanted to give others a heads up….

  6. Hi Sally,
    I am planning to make this cake for a party. I was wondering if you would recommend substituting cake flour for all or part of the all purpose? What effect would this have on the texture of the cake? Thank you for the recipe!

    1. Hi Victoria! Cake flour isn’t strong or sturdy enough for this chocolate cake. Cocoa powder already lightens up the crumb enough, so you need all-purpose to help stabilize it.

  7. Hi Sally,
    Can’t wait to make this cake . English being my second language , I sometimes ( often) misunderstand instructions .
    Is it Ok to make the cake with mousse and ganache and freeze it ? Or do I need to freeze the cake part only and do the rest a couple of days prior to put it together ?
    Also I have a « killer » mousse recipe I have been making for years .it is done with eggs , a combo of milk and dark chocolate , sugar and whipping cream . It is quite thick and intense Probably more than yours because of the eggs I am tempted to use it for this cake . What is your advice ?

    1. Hi Sonia, I recommend wrapping the individual baked and cooled cake layers tightly and freezing them up to 3 months. Then make the other two parts and assemble before serving. If you have a mousse recipe that you love then you can definitely use that in the cake!

  8. Thank you Sally for your prompt response . Will let u know how it turns out and will rate the cake . I can already predict it will be a5 stars…
    Sonia

  9. Hi Sally!
    As I only have 2 cake pans, I was wondering whether I could divide the batter between the 2 and cut the baked cakes in order to create 4 layers. What do you think?
    Thanks,
    Claire

    1. You can prepare this cake as a 3 layer cake (see recipe notes), but it would be too much batter for only 2 layers. They likely wouldn’t bake properly with too much batter in each pan.

      1. Thanks for the advice! I made the cake layers in 3 pans and it worked out fine!
        Just a comment regarding the ganache – it turned out very thin and when I poured it on the cake it flowed everywhere on to the work surface, leaving only a thin layer on the cake itself…so I’m wondering if I should have chilled it in the fridge before use? I waited the 20 mins you suggest in the recipe. The cake was still delicious though!!!

      2. Hi Claire! So glad it all worked out. Letting the ganache set for longer– or in the refrigerator– will allow it to thicken if it’s too thin after 20 minutes.

  10. I made this cake – which was sooo delicious and easy to make. The mousse was really good. I’m so glad you gave so much advice on using the different chocolates because it does make a difference. Now the ganache was good ( I used Guittard semi sweet wafers and some Ghiardelli semi sweet choco chips ) but it was on the thin side. My error may have been not chopping up fine or not enough chocolate. It tasted fine but I’ll be more careful the next time. Everyone raved about the cake and I must admit it had a delicious chocolate flavor . I wasn’t sure that I would like a dark chocolate cake but it was the best I ever tasted.

    1. Hi Vanessa! You can make the ganache ahead of time. Cover tightly and store ganache in the refrigerator for up to 5 days. Gently warm it to thin it out if needed.

  11. Hi Sally,

    Not sure if you would get time to look at my comment, but, one of my friend wanted me to make this as a 11 inch cake, and I’m not sure how to modify the ingredients. Would you please help me.

  12. I am hoping to make this next week for my bday, but instead of topping with ganache, I’d like to use your chocolate buttercream, and to pipe vanilla buttercream roses. Do you have any suggestions of things I should do differently, taking that approach?

    1. Hi Samantha, You don’t need to make any other changes. It sounds like it will be a beautiful cake. Happy birthday to you!

  13. I made this cake for my father’s birthday. The cake was superb. One of the best I’ve made.

    I only had 2 nine inch pans so I made two cakes and cooked them until the toothpick came out clean ~30 minutes. I let the cakes cool completely before cutting them in half to make the four layers of cake. The cake was moist and delicious. I added 1 cup of dark chocolate chips to the cake batter instead of the semi-sweet chips. I brewed 1/2 cup of Ethiopian espresso coffee which I used as my liquid and I used 1/2 a cup of 1% milk with 1 Tbsp vinegar in place of the buttermilk.

    The mousse filling was incredible. Light and delicious and I let the ganache drip down the sides like a drip cake. I saved some chocolate shavings for decoration.

    Thank you for posting such an incredible recipe. Love, Love, Love!

  14. Tried this yesterday, absolutely delicious!
    I used 3/4 100% natural cocoa powder and 1/4 dutch processed cocoa
    I do feel like the cake that I baked seems to be on the flimsy side, and sticky on top. is that normal? should I have used more flour to have more firm consistency?
    The reason I would like lit a bit more firm is to make it easier to work with while stacking it.
    Thanks for the recipe!

    1. Hi Jeannie! That’s a normal texture for this cake– it’s soft with deep flavor. You can try adding a little more flour to make it a bit sturdier if desired. Thank you so much!

  15. My cake was covered with your milk chocolate buttercream instead of the ganache since it was decorated for toddler’s bday but OMG that mousse is to die for. Everyone wants me to make their bday cakes now! Thank you Sally! We will definitely be making this mousse as a filling again and I already have made your buttercream, ganache and triple chocolate cake multiple times and always get raving feedback!

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