Dark Chocolate Mousse Layer Cake

5 from 3 votes

Indulge in the ultimate chocolate lover's dream: a Dark Chocolate Mousse Layer Cake. Perfect for satisfying your deepest chocolate cravings.

Prep Time2 30

Cook Time25

Refrigeration Time3

Total Time5 55

Course: Cakes, Christmas, Dessert, Valentines

Cuisine: American

Servings:

Calories: 509kcal

Author: Susan Ensley

Preheat oven to 350°F. Spray four 9-inch round cake pans with non-stick baking spray with flour and line with parchment paper. Set the pans aside until ready to use.
In a large bowl, whisk together all-purpose flour, sugar, baking powder, baking soda, salt, and cocoa powder. Set the bowl aside until ready to use.
In a medium size bowl with a spout³ whisk together sour cream, vegetable oil, and large eggs. Then, add the buttermilk and vanilla extract, whisk until well emulsified.
Pour the wet ingredients into the dry ingredients, then use a silicone spatula to stir them together until well combined. Next, add very hot tap water and stir with the spatula until well combined.
Use a large ice cream scoop to evenly divide the batter between the prepared cake pans. Place two pans offset on the lower rack of the oven and the other two pans offset on the upper rack, so that they are not directly above the pans below. Bake for 19-23 minutes, or until a toothpick inserted in the center comes out clean.
Remove the pans from the oven and place on wire cooling racks. Allow the cakes to cool completely in the pans.

While the cakes are cooling, prepare the chocolate mousse. Place cocoa powder in a small bowl and whisk in very hot tap water. Set the bowl aside until ready to use.
Place chocolate chips in a microwave-proof bowl and heat for 30 seconds, stirring after each heating, until the chips are melted. This should take about 2-3 minutes. Pour the cocoa powder mixture into the melted chocolate and stir with a silicone spatula until well combined. Set aside and allow it to cool slightly while whipping the cream.
Place the cold heavy whipping cream, powdered sugar, and vanilla extract in a large bowl. Use an electric hand mixer to beat on medium-high until medium peaks⁴ form. This should take 3-4 minutes.
Pour the chocolate mixture into the whipped cream. Use a silicone spatula to gently fold the chocolate mixture into the whipped cream. Avoid over-mixing, which can deflate/thin out the mousse. Cover the bowl and refrigerate for at least 2 hours and up to two days.⁵

Remove the cakes from the pans and peel the parchment off the bottoms. Remove about ½ cup of chocolate mousse from the bowl and set it aside for the crumb coat.⁶ Place one cake layer, right side up, on a cardboard cake round and about 1 ½ cups of chocolate mousse on top of the cake. Use an offset icing spatula to gently spread the mousse into an even layer. Then, place a second cake layer, upside down, on top of the chocolate mousse and spread about 1 ½ cups of chocolate mousse on top of the cake. Place a third cake layer, right side up, and spread 1 ½ cups of mousse on top of it.
Place the fourth cake layer upside down on top of the chocolate mousse. Then, spread the reserved chocolate mousse all over the cake to create a crumb coat. Place the cake uncovered in the refrigerator for at least an hour, and up to four hours to thoroughly chill before topping with chocolate ganache.

You should make the ganache after you have assembled the cake because it will need time to set up in the refrigerator. Place chocolate chips in a medium microwave-proof bowl and pour heavy whipping cream over them. Heat in the microwave in 30-second intervals, stirring well with a silicone spatula after each heating, until the chocolate is melted. This should take about 2 minutes.
Once the chips are melted, switch to a small whisk to fully emulsify the ganache. Set the bowl aside for 20 minutes to allow it to cool, whisking the ganache every five minutes or so.

Once the ganache has cooled for about 20 minutes, remove the cake from the refrigerator. Spoon the ganache over the top of the cake, allowing it to slightly run down the sides of the cake. Take care not to let too much run down the sides at once, or it will pool up around the bottom of the cake.⁷
Use an offset icing spatula, in an upward motion, to begin smoothing the ganache that has dripped down the sides of the cake. Continue spooning the ganache on the top and smoothing the drippings down the sides until you have used all of the ganache and the sides of the cake are completely covered.
Sprinkle some shaved chocolate on top of the cake.⁸ Chill the cake uncovered for 4-6 hours before serving. Then store in an airtight container in the refrigerator for up to five days.
Yield 16 servings

I used Ghirardelli 100% Dutch Process Cocoa.
You can substitute semi-sweet chocolate chips.
I used my 4-cup Pyrex measuring cup.
Medium peaks are between soft/loose peaks and stiff peaks
I like to refrigerate the mousse overnight and assemble the cake the next day. If you decide to do this, make sure to cover the cake layers overnight.
To help make sure you have an even amount of chocolate mousse between each layer and enough for the crumb coat, divide the mousse into four bowls before beginning to assemble the cake. Place about ½ cup into one bowl for the crumb coat, then divide the remaining mousse between three bowls for in between the cake layers.
Use a damp paper towel to wipe away any excess ganache that has pooled around the bottom of the cake.
To make shaved chocolate run a vegetable peeler along the edge of a high quality chocolate bar, such as Ghirardelli or Lindt.