Triple Chocolate Mousse Cake

Yesterday was my birthday. The awesome things about birthdays are that I get to plan my menu and choose whatever I want, guilt free. It gives me the opportunity to try some recipes I've had sitting around that were deemed too rich for most occasions (especially since I'm usually cooking for two, without anyone nearby to foist leftovers on). It's not just about eating what I want, but getting the opportunity to make it.

So I went for the triple chocolate mousse cake. The one that took the better part of the afternoon to make, using most of the bowls in our kitchen more than once. It was awesome (and will be for the better part of the week, I'd imagine - we're not finishing that baby any time soon). And it was fun. I got to test my mettle with a variety of different techniques, all but one of which were successful (you'll hear about my issues with the second layer in a bit). This was the first time I'd ever worked with gelatin, and that went extremely well - just look at that velvety smooth top layer!

Props to Jeff who chopped so much chocolate he developed a blister from the knife.

I made sure to buy excellent chocolate for the occasion. We used Callebaut 66% bittersweet and Mitica 44% milk chocolate. I'd never heard of Mitica before - I was buying bulk blocks of chocolate from Whole Foods and it was the only milk chocolate sold that way. I knew the Callebaut would be deliciously dark and bitter - perfect for baking. What I didn't know was that the Mitica milk chocolate would be so delightful! I thought it tasted almost like butterscotch - I have since found a website that claims it has toffee and caramel notes. Either way, it made a gorgeous mousse. As I read the recipe, I realized that the top layer was originally supposed to be white chocolate - it was changed by the blogger who I got the recipe from. I love white chocolate and would have probably chosen that route if I'd noticed sooner. But I'm glad I didn't, because I got to try a delicious new milk chocolate instead. I think that layer would be great as a stand-alone mousse dessert. I'll have to try it sometime.

If you're going to try this recipe, I would recommend choosing a day when you have plenty of free time. It takes quite a while, if you're slow like me. I also have a recommendation for the second layer, which I messed up. The first layer involves melting chocolate and butter, then integrating it into whipped egg whites. No problem. The second layer involves the same thing, except you're integrating melted chocolate into whipped cream. It seems like it will be the same process, but my experience says differently. I let my chocolate cool for about five minutes, like with the first layer, but I think that made it too cool. It was incredibly difficult to integrate into the cream, and, in fact, I did not totally succeed - my middle layer has some nice chunks of chocolate all through it. I think that mixing it with the cold cream caused the chocolate to harden too quickly, so that it could no longer integrate with the rest of the mixture. This wasn't a problem in the first layer, where the melted chocolate was mixed with other things before integration. Next time, I think I would whip the cream while the chocolate was melting and only let the chocolate cool for a minute or so before combining the two.

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

3/4 tsp instant espresso powder (I left this out, as I usually do, because I hate coffee flavors - I think this is why my two bottom layers ended up quite similar colors, instead of a pretty gradient)

1 1/2 tsp vanilla extract

4 large eggs, separated

pinch of salt

1/3 c light brown sugar

Bittersweet Chocolate Mousse (middle layer):

2 tbsp cocoa powder

5 tbsp hot water (I got mine out of the double boiler I used for the first layer)

7 oz bittersweet chocolate, finely chopped

1 1/2 c heavy cream

1 tbsp sugar

pinch of salt

Milk Chocolate Mousse (top layer):

3/4 tsp powdered gelatin

1 tbsp water

6 oz milk chocolate, finely chopped

1 1/2 c heavy cream, divided

Bottom Layer:

Butter the bottom and sides of a 9" springform pan (parchment paper on the bottom is helpful, too). Center a rack in the oven and preheat to 325°. Combine the butter, chocolate and espresso powder in a double boiler (in my case, just a metal bowl set over a pot of boiling water).

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).

Middle layer:
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 your stand mixer (hopefully you've cleaned the bowl since the first round), whip the cream, sugar and salt on medium speed until the mixture thickens, about 30 seconds (this can also be started while your chocolate is melting, to speed things along). Increase the speed to high and whip 30-60 seconds, until soft peaks form. Whisk in the cocoa powder mixture until smooth.

Then, add one third of the cream mixture to the melted chocolate and whisk in (again, this is to lighten it up, to facilitate folding the rest of the cream in). Fold in the remaining cream gently with a rubber spatula until no streaks remain.

Spread the mousse over the cake layer in your springform pan. Use a spatula to smooth out the top, and be sure to wipe any smears on the sides of the pan - they'll show up on the top layer later on. Refrigerate for 15 minutes before adding the top layer.

Top layer:
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.