Triple Chocolate Mousse Cake

submitted by Heather

 If you have any kind of event that you need to bring dessert to, go and make this cake now.  You will immediately become famous within that circle of friends and they will hail you queen/king of amazing chocolate cake confections.  Or if you don't have any occasion for which to make a fancy dessert, I still strongly urge you to make this cake and then bring slices to those lucky neighbors and friends who live close enough to get a piece before you polish it off yourself.  Yes, it's pretty rich.  Did that stop me from having 3 pieces in one day?  Let's not answer that.  And please excuse the messy cake plate.  Everyone was impatient to get their cake and I had to take this on the fly.

This cake has three layers of chocolate goodness.  Okay, for you chocolate purists, white chocolate isn't technically chocolate, but it's still very tasty.  Especially if you get the good kind with cocoa butter as an ingredient.  The bottom layer is a flourless chocolate cake that just melts in your mouth.  The middle layer consists of deep, dark chocolate and whipping cream, which solidify into a lovely, smooth mousse.  And the top, white layer is smooth and creamy and just the right addition to cut some of the richness of the dark chocolate. Which allows you to eat more than one piece.

Aren't those layers cool? This cake may look like a lot of work, but believe me, it's worth it.  None of the steps are difficult, they just take time.  I made the cake the day before serving it for my friend Janet's birthday, and it was perfect. Now, go get some whipping cream and chocolate and make this cake!

Triple Chocolate Mousse Cake

Ingredients:
For the bottom layer:
6 tbsp. unsalted butter, cut into 6 pieces
7 oz. bittersweet chocolate, finely chopped
1½ tsp. vanilla extract
4 large eggs, separated
Pinch of salt
1/3 cup light brown sugar, packed

For the middle layer:
2 tbsp. cocoa powder, preferably Dutch-processed
5 tbsp. hot water
7 oz. bittersweet chocolate, finely chopped
1½ cups heavy cream
1 tbsp. granulated sugar
Pinch of salt

For the top layer:
¾ tsp. powdered gelatin
1 tbsp. water
6 oz. white chocolate, finely chopped
1½ cups heavy cream

For garnish:
Chocolate curls or cocoa powder

Directions:
To make the bottom layer, butter the bottom only of a 9-inch springform pan.  (I used Baker's Joy instead of butter).  Center a rack in the oven and preheat to 325˚ F.  Combine the butter and chocolate in a large heatproof bowl set over simmering water.  Stir occasionally until the mixture is smooth. Or if you don't want to use a double boiler, you can melt the butter and chocolate together in the microwave, in 30 second increments, stirring each time. Remove from the heat and let cool slightly, about 5 minutes.   Whisk in the vanilla and egg yolks.  Set aside.

In a stand mixer fitted with the whisk attachment, beat the egg whites and salt on medium speed until foamy, about 30 seconds.  Crumble half of the brown sugar into the mixing bowl with your fingers to remove any lumps.  Beat until incorporated, about 15 seconds.  Add the remaining brown sugar and continue to beat on high speed until stiff peaks form, about 1 minute more.  Using a whisk, mix one-third of the beaten egg whites to the chocolate mixture to lighten it.  Fold in the remaining egg whites gently with a rubber spatula until no streaks remain.  Pour the batter into the prepared springform pan and smooth the top with a spatula.

Bake until the cake has risen, is firm around the edges and the center has just set but is still soft (should spring back after pressing gently with a finger), about 14-18 minutes.  Transfer the cake to a wire rack to cool completely, at least 1 hour.  Do not remove the cake from the pan.  (If not making the second layer right away, cover with plastic wrap and refrigerate until ready to proceed.)

To make the second layer, whisk together the cocoa powder and hot water in a small bowl; set aside.  Melt the chocolate in a heatproof bowl set over simmering water, stirring occasionally until smooth.  Once melted, remove from the heat and let cool slightly, 2-5 minutes.

In the clean bowl of a stand mixer fitted with the whisk attachment, whip the cream, sugar and salt on medium speed until the mixture begins to thicken, about 30 seconds.  Increase the speed to high and whip until soft peaks form when the whisk is lifted, 30-60 seconds.  Whisk in the cocoa powder mixture until smooth.  Using a whisk, mix one-third of the whipped cream to the chocolate mixture to lighten it.  Fold in the remaining whipped cream gently with a rubber spatula until no streaks remain.  Pour the mousse into the springform pan over the cooled cake and tap gently on the counter 3 times to remove air bubbles.  Gently smooth the top with a spatula.  Wipe the inside edge of the pan to remove any drips.  Refrigerate for at least 15 minutes while preparing the top layer.

To make the top layer, sprinkle the gelatin over the water in a small bowl and let stand at least 5 minutes to soften.  Place the white chocolate in a medium bowl.  Bring ½ cup of the 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 white chocolate and let stand about 1 minute.  Whisk until the mixture is smooth.  Cool to room temperature, about 5-8 minutes, stirring occasionally.

In the clean bowl of a stand mixer fitted with the whisk attachment, whip the remaining 1 cup of cream at medium speed until it begins to thicken.  Increase the speed to high and whip until soft peaks form when the whisk is lifted, 30-60 seconds.  Using a whisk, mix one-third of the whipped cream to the white chocolate mixture to lighten it.  Fold in the remaining whipped cream gently with a rubber spatula until no streaks remain.  Spoon the white chocolate mousse into the pan over the middle layer.  Smooth the top with an offset spatula.  Place a plate or something similar over the cake pan, instead of plastic wrap, to preserve it's freshness and not mar the smooth top.  Return the cake to the refrigerator and chill until set, at least 2½ hours. 

Source: adapted from annieseats.com, who adapted it from Cook’s Illustrated, November/December 2009