Almost-Famous Chocolate Mousse Cake

Ingredients

• 18.3 ounce devil's food cake mix plus required ingredients
• 12 ounces bittersweet chocolate chopped
• 14 ounces bittersweet chocolate chopped
• 5 tablespoons plus light
• 10 large eggs separated
• 0.8 cup heavy cream 
• 1.5 cups heavy cream cold
• 2 cups heavy cream cold
• 0.5 teaspoon salt 
• 0.3 cup strong coffee decoction 
• 1 tablespoon sugar 
• 1.5 cups sugar 
• 2 tablespoons butter unsalted
• 1 teaspoon vanilla extract 
• 1 pint whipped cream 

Equipment

• bowl
• frying pan
• baking sheet
• sauce pan
• oven
• knife
• whisk
• blender
• plastic wrap
• cake form
• microwave
• serrated knife

Directions

1. Make the cake: Prepare the cake mix as the label directs for a 9-by-13-inch cake.
2. Bake; cool slightly in the pan, then invert onto a rack to cool completely.
3. Clean out the cake pan and line it with plastic wrap.
4. Cut the cake in half lengthwise, then in thirds crosswise to make 6 rectangles. Using a serrated knife, slice each rectangle in half to make two layers. Arrange half of the pieces snugly in the cake pan. Crumble the remaining pieces and press tightly into 6 small balls; arrange 1 cake ball in the center of each cake rectangle in the pan.
5. Heat the chocolate, butter, coffee and 1/4 cup water in a heatproof bowl set over a saucepan of simmering water (do not let the bowl touch the water), stirring, until melted.
6. Remove the bowl from the pan; stir until cool. Reserve the simmering water. Fill a large bowl with ice water.
7. Whisk the egg yolks, 1 1/2 cups sugar and 2 tablespoons water in a separate large heatproof bowl. Set the bowl over the saucepan of simmering water and whisk until pale yellow, 6 to 8 minutes.
8. Add the chocolate-coffee mixture and the vanilla and whisk until combined, about 2 minutes.
9. Remove the bowl from the pan and set in the bowl of ice water; whisk until slightly cool but not thick, about 4 minutes.
10. Beat the egg whites and salt in a bowl with a mixer until foamy.
11. Add 2 tablespoons sugar and beat until almost stiff; gently fold into the chocolate-yolk mixture to make a dark chocolate mousse.
12. Spread 5 cups over the cake and cake balls. Freeze until firm on top, about 30 minutes.
13. Beat the heavy cream and the remaining 4 tablespoons sugar until soft peaks form; fold into the remaining mousse.
14. Remove the cake from the freezer; spread with the light chocolate mousse, cover with plastic wrap and freeze until firm, at least 6 hours or overnight.
15. Make the chocolate shell: Stir the chocolate, heavy cream and 4 tablespoons corn syrup in a heatproof bowl set over a saucepan of simmering water (do not let the bowl touch the water) until melted. A spoonful at a time, spread half of the shell mixture over the frozen mousse. Return to the freezer.
16. Add the remaining 1 tablespoon corn syrup and the butter to the remaining chocolate shell mixture. Microwave 30 seconds, then stir until glossy.
17. To serve the cake, beat the heavy cream with a mixer until foamy.
18. Add the sugar and beat until soft peaks form.
19. Remove the cake from the freezer; invert onto a baking sheet and unmold, then invert again onto a platter, chocolate shell-side up.
20. Cut the cake in half lengthwise using a warm knife, then cut into thirds crosswise to make 6 rectangles; cut each rectangle in half diagonally to make 2 triangles. Top each triangle with whipped cream, ice cream and the prepared chocolate sauce.
21. Photograph by Kang Kim