For the Cake

Cup of Yum
1. Prepare ½ package of cake mix according to the instructions on the box. The above ingredient measurements are for ½ box of Betty Crocker Devil's Food Cake, so be sure to use halved measurements for the appropriate ingredients if you use a different brand of cake mix. If your cake mix calls for 3 eggs, use 1 egg and 1 egg yolk as your halved measurement. Bake in a 9-inch springform pan according to the instructions (around 25 minutes) and let cool on a wire rack while you prepare the mousse.

For the Chocolate Mousse

1. In a small bowl, combine the gelatin and cold water and bloom for 5-10 minutes.
2. Meanwhile, place chocolate chips in a heatproof bowl. In a small saucepan set over medium-high heat, bring 1 cup of heavy cream to a simmer (between 112-115°F), then remove from the heat.
3. Whisk in the bloomed gelatin and stir until completely dissolved. Pour mixture over the chocolate chips and whisk until melted and combined. Allow mixture to cool, stirring occasionally.
4. In the bowl of a stand mixer fitted with the whisk attachment, or with a hand mixer in a large bowl, beat the remaining 2 cups of cream with the powdered sugar until stiff peaks form.
5. Stir about ¼ cup of the whipped cream into the melted chocolate. Gently fold in the remaining whipped cream until fully incorporated.
6. Spread the chocolate mousse evenly on top of the cooled cake while still inside the pan.
7. Cover with plastic wrap and refrigerate for at least 8 hours or up to overnight.

For the Ganache

1. Once the cake has chilled overnight, place the chocolate chips in a heatproof bowl. In a small saucepan set over medium-high heat, bring 1 cup of heavy cream to a simmer (between 112-115°F), then remove from the heat.
2. Pour the warm cream over chocolate chips and allow to sit for 3-4 minutes, then whisk gently until smooth and shiny. Allow to cool until slightly thickened, then pour over the mousse.
3. Cover and chill for 1 hour. Serve garnished with chocolate shavings and berries, if desired.