Triple Chocolate Mousse Cake

Do you ever see something and just HAVE to have it, or more specifically, do you ever see a recipe and just HAVE to make it? This happens to me pretty frequently while perusing food magazines, scanning Web sites, flipping through cookbooks, watching The Food Network, and so on. Most recently it happened while I was standing in the checkout line at Whole Foods. There in front of me was the latest issue of Cook's Illustrated, and there on the cover was the most decadent-looking chocolate mousse cake. I talked myself down from buying the issue -- reminding myself that I had recently signed up for an online membership to CI and would surely find the recipe there. When I got home, I put away the groceries more quickly than I ever have, jumped on my computer, and started searching CI's site. Sure enough, the recipe was there.

I read through it, checking out what each of the mouthwatering components consists of -- the bottom layer is a flourless chocolate cake, the middle is chocolate mousse, and the top is white chocolate mousse. Adorn it all with some chocolate curls, and you've got yourself one show-stopping dessert! I brought it to Jeff's parents' house for Passover, and the empty pan I returned home with was a measure of the true success of this cake.

Oh, but let me go on a short tangent about the pan. This cake uses a springform pan, so the sides can be taken off, leaving the cake on the bottom part of the pan to serve it. Trying to flip a cake like this out of a regular pan would just make a huge mess. Unfortunately, I didn't own a springform pan, just some small individual ones, so I had to go shopping for one. Actually, I guess that's not too unfortunate!

Jeff and I were heading back from bringing our winter clothes to storage (our storage unit is way outside of the city -- to save money), and I convinced him to stop at the Williams-Sonoma in Hingham, so I could get the pan before we cut it too close to when I planned to make the cake.

I don't know why, but I hadn't expected Williams-Sonoma to have springform pans in three different sizes. I stood there, staring at the pans, trying to decide which one to get -- because I didn't think to check that when I initially looked at the recipe -- when a sales associate came over. I asked her what size is most commonly used in recipes and somehow started talking about the chocolate mousse cake. Suddenly, she stopped me and asked if I was referring to the cake on the cover of Cook's Illustrated, and I said yes, that's the one! I was so surprised she knew about it (but since then I've come to find out that several other people saw that cake, and it stuck in their heads too.) She couldn't remember what size it was either, so Jeff started trying to get on the Cook's Illustrated site on his phone. As we were struggling to get mobile technology to work quickly and efficiently (it never does, does it?), the sales associate returned and told me it needed a 9.5-inch pan. She had called her mom and asked her to look in the magazine! This is just one of the many reasons I love Williams-Sonoma.Where else can you find people who care that much about cooking and baking?

So now that I knew I needed a 9.5-inch pan, we looked back at the three sizes there, which were 8, 9, or 10 inches. Now, isn't that just too funny? So the sales associate and I talked it over for a few minutes, and I decided to go with the 9-inch pan. It worked out perfectly.

Below is the recipe, rewritten for how I made this cake. I eliminated nitpicky things like double boilers. I never use a double boiler when I can just microwave. It's so silly to go through all that trouble. You can find the complete, original recipe on Cook's Illustrated's Web site. What's that you say? You still don't have a subscription... after all these CI recipes I've told you about? What are you waiting for? There's even a great step-by-step video that shows you how to make this cake and how to cut it so you don't ruin the layers.

Triple Chocolate Mousse Cake (adapted from Cook's Illustrated, November 2009)
(Printable version)


Bottom Layer

6 tablespoons (3/4 stick) unsalted butter , cut into 6 pieces, plus extra for greasing pan
7 ounces bittersweet chocolate , chopped fine (Ghirardelli Bittersweet Chocolate Baking Bar)
3/4 teaspoon instant espresso powder
1 1/2 teaspoons vanilla extract
4 large eggs, separated
Pinch table salt
1/3 cup packed light brown sugar

Middle Layer

2 tablespoons Dutch-processed cocoa powder
5 tablespoons hot water
7 ounces bittersweet chocolate, chopped fine (Ghirardelli Bittersweet Chocolate Baking Bar)
1 1/2 cups cold heavy cream
1 tablespoon granulated sugar
1/8 teaspoon table salt

Top Layer

3/4 teaspoon powdered gelatin
1 tablespoon water
6 ounces white chocolate chips (Valrhona discs)
1 1/2 cups cold heavy cream
Block of Callebaut bittersweet chocolate (for making chocolate curls or shavings), optional


Bottom Layer

Preheat oven to 325 degrees. Butter bottom and sides of 9-inch springform pan. Melt butter and chocolate in medium bowl in microwave. (I originally melted the chocolate in a Pyrex measuring cup and then transferred it to a bowl. It's easier to just put it in a medium bowl to begin with.)

Stir in espresso powder. Cool slightly. Whisk in vanilla and egg yolks; set aside.

In stand mixer fitted with whisk attachment, beat egg whites and salt at medium speed until frothy, about 30 seconds. Add half of brown sugar and beat until combined, about 15 seconds. Add remaining brown sugar and beat at high speed until soft peaks form when whisk is lifted, about 1 minute longer, scraping down sides halfway through.

Using a whisk, fold one-third of beaten egg whites into chocolate mixture to lighten. Using a rubber spatula, fold in remaining egg whites until no white streaks remain. Pour batter into prepared springform pan, and smooth the top with a small offset spatula.

Bake until cake has risen, is firm around edges, and center has just set but is still soft (center of cake will spring back after pressing gently with finger), 13 to 18 minutes. (Watch closely. Mine was done at just 13 minutes. And don't doubt yourself. If the edges are firm and the cake springs back, it's done.)

Transfer cake to wire rack to cool completely, about 1 hour. (Cake will collapse as it cools. It's actually crazy how much it sinks!) Do not remove cake from pan.

Middle Layer

Combine cocoa powder and hot water in small bowl; set aside. Melt chocolate in medium bowl in microwave. Cool slightly.

In clean bowl of stand mixer fitted with whisk attachment, whip cream, granulated sugar, and salt at medium speed until mixture begins to thicken, about 30 seconds. Increase speed to high and whip until soft peaks form when whisk is lifted.

Whisk cocoa powder mixture into melted chocolate until smooth. Using whisk, fold one-third of whipped cream into chocolate mixture to lighten.

Using a rubber spatula, fold in remaining whipped cream until no white streaks remain.

Spoon mousse into springform pan over cooled cake and gently tap pan on counter three times to remove any large air bubbles; gently smooth top with offset spatula. Carefully clean any drips from the inside edges of the pan. Refrigerate cake at least 15 minutes while preparing top layer.

Top Layer

In small bowl, sprinkle gelatin over water; let stand at least 5 minutes.

Place white chocolate in medium bowl.

Bring ½ cup cream to simmer in small saucepan over medium-high heat. Remove from heat; add gelatin mixture and stir until fully dissolved. Pour cream mixture over white chocolate and whisk until chocolate is melted and mixture is smooth. Cool to room temperature, stirring occasionally, 5 to 8 minutes (mixture will thicken slightly).

In clean bowl of stand mixer fitted with whisk attachment, whip remaining cup cream at medium speed until it begins to thicken, about 30 seconds. Increase speed to high and whip until soft peaks form when whisk is lifted. Using a whisk, fold one-third of whipped cream into white chocolate mixture to lighten.

Using a rubber spatula, fold remaining whipped cream into white chocolate mixture until no white streaks remain. Spoon white chocolate mousse into pan over middle layer. Smooth top with offset spatula. Return cake to refrigerator and chill until set, at least 2½ hours. (I left it in the fridge overnight.)

To Serve

Take cake out of fridge 45 minutes before serving. Using the back of a paring knife, scrape along the edge of a block of chocolate to form chocolate shavings or curls.

Sprinkle these on top of the cake.

Run an offset between cake and side of springform pan; remove side of pan.

Clean and smooth the edges of the cake by running an offset around the cake.

Using a knife dipped in hot water, cut the cake into slices, Clean and rewarm the knife after each cut. Serve with a dollop of homemade whipped cream.

The bottom layer was amazing. I've made a few flourless chocolate cakes before, and I've always loved how moist they are. But because this one gets completely covered with chocolate mousse after it cools, I think it stayed even more moist than a plain flourless chocolate cake would. There was no way the edges could dry out.

The middle layer was my absolute favorite. It's the most amazing dark chocolate mousse. I even saved a little for myself. I mean my pan was a 1/2-inch too small. I couldn't possibly fit all the mousse in there. (Truth be told, I could, but then I'd have no leftover mousse to snack on!)

The top layer I could do without, but everyone else loved it. Let me explain. I despise white chocolate. It's not even really chocolate! (It doesn't contain any cocoa solids, which would technically constitute chocolate, and it's just sickeningly sweet and plastic-like if you ask me.) But when I make recipes, I usually follow them to a T and improvise the next time. So I made the white chocolate mousse knowing I probably wouldn't like it. I even bought Valrhona white chocolate discs at $16.99 per pound because I thought if I went with expensive white chocolate, that would help. It didn't. (CI recommends Guittard Choc-Au-Lait White Chips, but of course Whole Foods had every other kind of Guittard chips but the ones I needed. I think they are usually there though.) Next time I make this, I'll definitely just do a layer of homemade whipped cream on top of the rich chocolate mousse and cake. That would be right up my alley. But I'm the only one who didn't really like it, and if you like white chocolate, I'm sure you'll love it.

What do you think of white chocolate?

What's the most decadent dessert you've ever made?