|Props to Jeff who chopped so much chocolate he developed a blister from the knife.|
Triple Chocolate Mousse Cake
Adapted slightly from Confections of a Serial Baker.
Flourless Chocolate Cake (bottom layer):
6 tbsp butter, cut into 6 pieces
7 oz bittersweet chocolate, finely chopped
Stir with a rubber spatula until the mixture is totally smooth.
Remove from the heat and let cool for about 5 minutes, then whisk in vanilla and egg yolks (don't disassemble your double boiler - you'll need it again. I turned the stove off and put a lid on my water to keep it warm). Set aside.
While the mixture is cooling, beat the egg whites in a stand mixer with whisk attachment on medium speed for 30 seconds, until foamy. Crumble in half the brown sugar (removing any lumps with your fingers) and beat 15 seconds until incorporated. Crumble in the rest of the brown sugar and beat on high speed until stiff peaks form (the instructions say 1 minute, but it definitely took me a few). Take one third of the egg white mixture and add it to the chocolate mixture, whisking until smooth (this is to lighten the chocolate mixture, to make folding easier). Then fold in the rest of the egg whites with a spatula until no streaks remain (fold gently - the goal is to keep as much air in those egg whites as you can manage). Pour the batter into the prepared springform pan.
Bake the cake until the edges are firm and the middle is set but soft (meaning that it will spring back when your finger touches it), about 14-18 minutes. Transfer cake (still in the pan!) to a wire rack and cool for at least 1 hour (the cake will deflate a bit as it cools).
In a small bowl, mix together the cocoa powder and hot water, then set aside. Melt the chocolate in the double boiler, stirring until smooth. Remove from the heat and cool slightly, 2-5 minutes (as I said above, I'd advocate a short cooling time, if possible).
In a small bowl, sprinkle the gelatin over the water. Let stand 5 minutes (the gelatin will absorb the water). Place the milk chocolate into a medium bowl. Bring 1/2 c cream to a boil in a small saucepan. Remove the pan from the heat, add the gelatin mixture and stir until dissolved. Pour the hot cream mixture over the chocolate and let stand a few seconds so the cream can begin to melt the chocolate. Then, whisk until the mixture is smooth. Cool for a few minutes (I just let it cool for as long as it took me to finish the next step).
In your (clean!) stand mixer with whisk attachment, whip the remaining 1 c of cream at medium speed until it thickens. Then increase the speed to high until soft peaks form. Whisk one third of the cream into the chocolate mixture, then fold in the rest with a rubber spatula until no streaks remain. Pour the mousse into the pan over the middle layer and smooth the top with a spatula.
Refrigerate the cake until all the layers are set, at least 2 1/2 hours.