Chocolate Mousse Cake Recipe

Begin by making the custard portion for the cream so it has time to cool. Whisk together the sugar and egg yolks in a bowl until they're pale and smooth.
50 grams granulated sugar, 3 large egg yolks room temperature
In a small saucepan, melt the butter and then while whisking the egg yolks, stream the hot butter in to temper the eggs.
113 grams unsalted butter
Return the whole mixture to the saucepan. Cook over medium-low heat, whisking continuously, until it thickens enough to coat the back of a spoon and resembles lemon curd, about 3-5 minutes.
Remove it from the heat, pour it back into the bowl and cover with a lid or plastic wrap. Set it aside to cool completely to room temperature.

Preheat the oven to 350F/177C and grease two 8-inch cake pans with baking spray and line the bottoms with parchment paper
In a large bowl or the bowl of a stand mixer, whisk together the flour, granulated sugar, cocoa powder, baking powder and salt until they're evenly distributed.
240 grams all-purpose flour spooned and leveled, 400 grams granulated sugar, 80 grams unsweetened cocoa powder spooned and leveled, 1 Tbsp baking powder, ½ tsp salt
Add the oil and use an electric mixer, at medium speed, to combine the mixture until the dry ingredients are fully coated.
180 mL canola oil or any neutral oil
Add the eggs, one at a time, beating on medium speed for 20 seconds each. Scrape the edge of the bowl, add in the sour cream and beat the mixture until it's well combined.
2 large eggs room temperature, 170 grams sour cream
Turn the mixer down to low speed and pour in the milk. Scrape the edge of the bowl and mix just until the batter is smooth.
180 mL milk room temperature
Distribute the batter evenly among both pans, about 22oz in each. Bake for 35-40 minutes, until the cake releases itself from the edge of the pan or springs back when you press on the center.
Allow the cakes to cool in the pan for a few minutes and then invert them onto a cooling rack or tea towel. Allow them to cool completely to room temperature and then slice each cake in half, to make four layers.

In a medium bowl, microwave the chocolate for 20 seconds, stir it and repeat until the chocolate is smooth. Set it aside to cool until it's no longer hot but still melted and runny.
170 grams dark chocolate chips melted
To make the whipped cream, place the heavy whipping cream, vanilla and powdered sugar in a large bowl or the bowl of a stand mixer. Use an electric mixer, at medium speed (so it doesn't splash), to beat the cream until it thickens slightly.
480 mL heavy whipping cream, 30 grams powdered sugar spooned and leveled, 1 tsp vanilla extract
Then increase the speed to high and whip until it forms stiff peaks.
Remove about 1/4 of the whipped cream, for the top of the cake, and then add the custard to the bowl.
Beat the custard and the whipped cream just until they're smooth and then add the cooled, melted chocolate and beat until it's fully combined.

Place the first layer of cake on a flat surface and use 1/3 of the chocolate cream to frost the first layer.
Repeat with the second and third layer and then place the fourth layer of cake on top. Frost with reserved whipped cream and use a grater to make chocolate shavings from a chocolate bar.
chocolate bar for shavings
Refrigerate the cake for several hours so the cream can set. Serve slightly chilled.