Dark Chocolate Mousse Cake

by 247tasty

Prep Time: 2 hrs 30 mins | Cook Time: 25 mins | Total Time: 5 hrs 55 mins | Yield: 10–12

This is the prettiest cake! Dark Chocolate Mousse Cake with layers of moist cake and simple chocolate mousse, then covered with semi-sweet chocolate ganache. Top the cake off with some fresh berries, and/or chocolate shavings making this beautiful cake fancier.


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

Chocolate Mousse:

two 4-oz quality semi-sweet chocolate bars (113 grams each), finely chopped
1/4 c (22 grams) unsweetened cocoa powder
2 cups (480ml) heavy cream or heavy whipping cream
1/2 c (120ml) hot water
1/2 tsp pure vanilla extract
2 tbsp (15 grams) confectioners’ sugar

Chocolate Ganache:
1 c (240ml) heavy cream or heavy whipping cream
two 4-oz quality semi-sweet chocolate bars (113 grams each), finely chopped*

How to make Dark Chocolate Mousse Cake

Step 1: Prepare the oven. Preheat it to 350 degrees F or 177 degrees C. Grease and line with parchment paper four 8 or 9-inch cake pans. Make sure to grease the parchment paper as well.

Step 2: In a large bowl, place the flour, cocoa powder, sugar, baking soda, baking powder, salt, and espresso powder (if using). Mix well and set aside. Combine the oil, eggs, and sour cream with a handheld or a stand mixer fitted with a whisk attachment on medium-high speed until well blended. Then, add the buttermilk along with the vanilla. Mix again until incorporated. Into the dry ingredients, pour the wet ingredients. Add the hot water/coffee and mix on low speed until the batter is well blended. If using, fold in the chocolate chips.

Step 3: Into the prepared pans, evenly divide the batter. Place in the preheated oven and bake for about 19 to 23 minutes or until a toothpick inserted in the center of the cake comes out clean. Note that the baking time of the cake varies so make sure to keep an eye on them while baking.

Step 4: When done, take the cakes out of the oven and onto a wire rack. Let the cakes cool fully in the pan.

Step 5: Meanwhile, ready the chocolate mousse (note that you can prep this about 1 to 2 days in advance). To start, mix the hot water and cocoa powder, then set aside. In a double boiler, melt the chopped chocolate bars. Alternately, you can melt the chocolate bars in the microwave. To do this, put the chopped chocolate bars in a medium heat-proof bowl and heat in the microwave in 20-second increments, stirring every after each increment until fully melted and smooth. Set aside. Whip the heavy cream with confectioners’ sugar, and vanilla extract using a hand mixer or a stand mixer fitted with a whisk attachment on medium-high speed for about 3 to 4 minutes until medium peaks form. Then, add the chocolate mixture and gently fold using a rubber spatula or spoon. DO NOT OVERMIX. Lastly, tent the mousse and place it in the fridge for at least 2 hours or up to 2 days.

Step 6: To assemble: Using a large serrated knife, level the cakes if needed. To do this, slice a thin layer off the top of the cake. This will create a flat surface. Discard the tops. On a cake stand or serving plate, place the first cake layer. Evenly cover the top with around 1 1/2 c chocolate mousse using a large icing spatula. Top it with another cake layer and evenly spread another 1 1/2 c chocolate mousse to cover the top. Place the third cake layer on top and evenly cover it with another 1 1/2 c mousse. For a thin crumb coat, reserve a large spoonful of mousse. Top the previous layer with the final cake and spread the rest of the mousse around the sides. To smooth out the crumb coat, run a bench scraper around the cake. Keep the cake in the fridge for at least 1 hour or up to 4 hours.

Step 7: To make the chocolate ganache, put the chopped chocolate in a medium heat-proof bowl. In a small saucepan, heat the cream over medium heat until it starts to gently simmer. Make sure to not let it come to a rapid boil. Then, pour this over the chopped chocolate and set it aside for about 2 to 3 minutes. After the said time, very slowly stir the chocolate using a metal spoon or small rubber spatula until the chocolate has completely melted and you have a smooth mixture. Allow the ganache to cool at room temperature for about 20 minutes.

Step 8: In the chilled cake, pour or spoon the ganache. Using an icing spatula, smooth the top, and with a bench scraper, smooth the sides. Top the cake with some fresh berries and/or chocolate shavings if desired.

Step 9: Slice and enjoy the cake right away. Or chill for up to 4 to 6 hours, uncovered, before serving. Note that this cake is amazing either chilled or at room temperature.

Step 10: Tightly cover any leftover cake and keep it in the fridge for up to 5 days.

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