Rich chocolate mousse and chewy brownies are wonderful by themselves, but put them together in a Chocolate Mousse Brownie Cake and the result is romance on a plate! Make a mini cake for Valentine's Day, Date Night, or when you just want a special treat to share.
Make the brownie base: Preheat the oven to 325 °F and spray a 6-inch round springform pan with baking spray.
In a microwave safe bowl, melt the butter with the sugar and sifted cocoa powder on HIGH in 30 second increments, stirring after each segment. Alternatively, melt them in a heavy-bottomed saucepan over low heat. Let cool for about 5 minutes.
Mix in the vanilla and salt, then add the egg.
Stir in the flour vigorously until well mixed, at least a minute. This develops the gluten so the brownie will be chewy.
Transfer the mixture to the prepared springform pan, and bake for 24 to 28 minutes. The brownies might be a little gooey in the center, but that's fine.
Let the brownie cool completely while you make the mousse.
Make the chocolate mousse: Chop the chocolate with a serrated knife (the edge grabs the chocolate better than a chef's knife). Also you can make decorative chocolate shavings with a vegetable peeler. Set both aside.
Beat the egg with the sugar for about 2 to 3 minutes with a hand mixer until it’s pale yellow and falls in ribbons when the beaters are lifted. Stir in ½ cup of the heavy cream just until combined.
Cook the egg mixture in a heavy-bottomed saucepan set over medium heat, stirring constantly. The mixture will start to thicken after about 3 to 4 minutes and will to coat the back of a spatula or spoon, but don't let it simmer or boil. Remove from heat. Thickening the mousse allows it to hold its shape when the dessert is released from the springform pan later.
Add the chopped chocolate to the pan, cover, and let sit for 2 minutes like you would for making ganache. Remove the lid and whisk until the chocolate has completely melted. Transfer the chocolate custard to a bowl and chill it for at least an hour to firm up.
Beat the remaining ½ cup of heavy cream in a clean bowl until soft peaks just start to form. This should be done at least an hour before you want to serve the cake.
Remove the chocolate custard from the refrigerator, and add small amounts to the whipped cream while beating until the mousse is smooth and fluffy. Stir the vanilla extract into the mousse.
Assemble the cake: Spoon the chocolate mousse on top of the brownie in the springform pan, smoothing the top, then refrigerate for at least an hour before serving.
When you're ready to serve, sprinkle the top with the reserved chocolate shavings. Run a knife around the edge of the pan (all the way down to the brownie layer) to release the cake from the pan. Remove the cake from the springform pan: place one hand under the pan, open the clasp, and let the rim of the pan fall onto your arm.
Carefully transfer the cake to a cake plate, serve, and enjoy!
Storage instructions: Chocolate Mousse Brownie Cake can be stored in the refrigerator (to keep the mousse firm) for up to a week.
Make-ahead instructions: The brownie base can be baked a day ahead and kept it at room temperature. Leave it in the pan, covered well in plastic wrap.The chocolate custard can be made a day ahead, tightly covered with plastic wrap and stored in the refrigerator.
Recipe Notes
Use a good quality semi-sweet or dark chocolate (between 60 to 72% cocoa) for the mousse (not chocolate chips). You can also use chocolate wafers if you don't want to top the mousse cake with chocolate shavings.You can use regular cocoa powder, or substitute dark chocolate cocoa powder for a more intense chocolate brownie.If you'd like, you can simply make the mousse and serve it in a bowl or individual ramekins. But really, chocolate mousse and brownie cake deserve to be together!If you don't have a 6-inch springform pan, use a 6-inch round baking pan, well sprayed with baking spray. To ease removing the cake later, make a sling out of 2 long, skinny pieces of parchment paper, placing them perpendicularly to each other in the cake pan. Then, line the pan with a parchment paper collar before pouring in the brownie batter. This will help to keep the mousse from sticking to the pan when you top the brownie layer. See the post for pictures of this method in use.For a full-sized cake, double the recipe ingredients and using a 9-inch round springform pan. Bake the brownie for about 3 to 5 minutes longer.