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

Print
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

 

292 Comments

  1. Delicious chocolate cake and soooo easy to make! I baked in a sheet and it took about 35 mins. This cake has the perfect texture. Thank you for the recipe. I made the chocolate mouse and it tastes delicious as well, but because I used everything dark chocolate it’s a bit bitter totally on my part we love it dark and bitter anyways!

  2. Hi Sally, I would like to make one of your chocolate cakes with your vanilla buttercream (from your favorite white cake recipe). Do you think this chocolate cake or your triple chocolate cake base would work better? I see the major difference is adding sour cream and using less coffee. Let me know what you think! Thanks!

    1. Hi Debra! Either will work– the flavor of the cakes is the exact same, but the added sour cream and reduced coffee in this version simply creates a thicker, sturdier crumb. Use either!

  3. Hi Sally,
    Can I do half recipe with 2 or 3 cake pans? This is my first attempt to make a fancy cake ( this is considered fancy for me as I only made cupcakes and cookies ( all your recipes).
    Thank you very much.
    Bunthida

  4. This cake looks amazing! Would you recommend this cake be sturdy enough to use for a four layer pinata cake with frosting over the whole thing?

    1. Hi Rebecca, This cake is so moist that I’m unsure if it would work as a piñata cake. If you try it be sure to fill up the center to the top with sprinkles or candies so that the top/4th layer has a surface to rest on so it doesn’t cave in. Let me know if you try it!

  5. Hi Sally,
    The cake turned out really well, and so did the mousse until I used it. It was a good consistency when I put it on the first layer, but as I began to build up, it started oozing out. I had to quickly put it in the fridge before the layers slipped off. Overall it tasted good, but I have no idea why the mousse did what it did. I used Ghirardelli chocolate chips, and not chocolate bars. Is that what went wrong?

    1. Hi Willow, I do recommend using pure chocolate here– not chocolate chips. What always helps is chilling the mousse, even if that means spreading the mousse onto the bottom layer– then chilling that mousse-topped layer– then adding the next layer on top. The refrigerator is your friend when it comes to assembling this cake! I hope this helps for next time.

  6. Made this cake this weekend and it was a HIT! Didn’t have time/space to bake 4 cake layers so I just kept the recipe as is and filled two 9’’ cake pans and cooked about 30 minutes. As such, I had extra frosting which I used as ‘sandwich’ filling in the chocolate chip cookie sandwiches that I circled the cake with. This was a massive hit!! Also noted that the 80% chocolate bars I bought were 3.5oz so I tossed some dark chocolate chips in and chopped them! Thanks for the great recipe!

  7. Hi Sally,
    Am I able to use this recipe for cupcakes? Or is the cake so moist that it will have trouble sticking to the liners?

  8. Sally-
    Thank you for such an outstanding recipe and thorough directions. I made the cake for Christmas Eve dinner and everyone loved it!!! I will definitely be making it again….I find myself longing for a piece on a daily basis – haha!
    Mary

  9. I made this cake for my birthday. It was absolutely delicious!!! I just made the mousse as the icing, and covered with berries. Super rich, chocolately and simple to make. Best chocolate cake I have made!

  10. I want to use this to make tea cakes/petit fours. To make it sturdier, should I replace all the buttermilk with sour cream, or just part of the buttermilk? I noticed it already calls for some sour cream. How much should I reduce the hot coffee by?

    1. Hi Megan! You can try replacing all of the buttermilk with extra sour cream to make a denser cake. No need to replace or reduce the hot liquid.

  11. I am planning to assemble the cake (cake and mousse) and refrigerate it overnight. The next day I will be making the ganache and pouring over the cake. My question is, should I pour the ganache over refrigerated cake or room-temperature cake. My concern is that since the heavy cream will be warm, it will “melt” the cake. Thanks!

    1. Hi Carolina, I always recommend pouring the ganache over a cold cake. Additionally you should let your ganache sit at room temperature for about 20 minutes to cool down so it won’t be super hot when it’s poured over the cake Enjoy!

  12. I loved it. I have finally found my go to chocolate cake receipe. So moist and delicious. I need to however work on my presentation skills. My mousse came out a little soft but thats because I was scared to over whip it.

  13. Oh my how you inspire me! I made this cake yesterday, I bake something for the office every week, and try so many of your recipes! This cake is sooooo good. I have made and had good cake before, but this is a whole other level of creamy chocolatey goodness. Thank you for sharing this one!

  14. Hi Sally,
    I was wondering where I could purchase the cake stand that you used in the picture. Thank you for the recipe! Looking forward to trying it soon!

    1. I will bake this cake after two days,but according to the mousse,i need to know the percentage of the coco in chocolate bars,i mean 50% coco, 60% coco?
      And is it ok to frost all the cake with the mousse,? I mean to put it as a filling ,on top and all around the cake.
      Thank you:)

  15. One of the best cakes I’ve ever made. Made this for my dad’s 60th. He was very impressed and it tasted amazing. Everything about it is great. Substituted the espresso powder for Green and Black’s cocoa powder and the coffee for Earl Grey tea – not a coffee person! Homemade buttermilk (not that common in UK). Unbelievably scrumptious! Every aspect was superb. Thanks a lot!

  16. Hi! I was thinking of using the chocolate mousse to do a crumb coat for a “naked cake” effect and then using the ganache to do a chocolate drip rather than coating the cake in the ganache. Do you think this would work well, or should I use icing rather than the mousse to created the naked look?

    1. Hi Lisa, Chocolate cake already has cocoa powder— which is a VERY fine dry ingredient. Unfortunately the combination of cake flour and cocoa powder usually results in a flimsy cake.

  17. What can I use instead of sour cream and buttermilk? Since I don’t have time to set the sour cream as I need to bake it today for my sons birthday As we in lockdown!! And I am not a baker at all!!

    1. Hi! Yogurt is always a fine substitution for sour cream. And you can use the buttermilk substitution listed in the recipe note Why Room Temperature?

  18. Thank you so much Sally! Am in Nepal in total lockdown and trying my hand at baking for the first time ‍♀️‍♀️Very ambitious hahha but it’s my sons birthday and no bakeries are open so a Mum’s gotta do what a mum’s gotta do I guess!!
    Appreciate it!! Stay safe!!

  19. Hi Sally! I would like to use this recipe but use a chocolate cake instead of this dark chocolate cake. Will the mousse and ganache taste good with a standard chocolate cake?

  20. Hi Sally

    I am planning to make this cake for my wife’s birthday in few days. trouble is i only have one cake baking tray. Someone above in the comments suggested pouring all batter in the tray and then cutting it when ready and you said it is not a good idea. Is it ok if i bake each layer one after another. what will happen to the batter if you leave it for long period of time (4th layer will be baked 2-2.5 hours after everything is mixed together). would that affect the sponges?

    Many thanks

    1. Hi Peter, I’m happy to help. You can let the unused batter sit at room temperature, covered, until the cake pan is ready to use again. Baking right away would be ideal for the cake’s texture, but this is the only way if you only have 1 pan.

  21. Hi I was bored being locked down and found your recipe. I didn’t have strawberries to decorate but trust me the cake came out so well and the family is enjoying it. Thanks for sharing your recipes. Appreciate it.

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