Triple Chocolate Mousse Cake

If you’re a chocolate lover or have someone in your life who is, you absolutely have to make them this cake. No doubt about it, one of the best desserts I’ve ever made and probably one of the most gorgeous too! Just look at those layers, I am seriously obsessed with them.

Ok, with that out of the way, let me back up a little. Back in August I was housesitting for Shane’s parents and made this cake for the first time. I only brought a few pieces home for Shane when I left, mostly because I wasn’t sure how easy it would be to transport in the car and whether it would hold up in the heat. Long story short, it survived the trip without issue. Upon taking his first bite, Shane immediately asked “so, where’s the rest of this cake?” He was not thrilled when I told him I’d left most of it for his parents. I’m pretty sure if I’d brought the entire cake back he would gladly have eaten the whole thing himself. To say he enjoyed it would be a serious understatement…

To make it up to him, I promised to make the cake again for his birthday. And so I did just that last Friday. We even shared a few pieces with my mom and step-dad – it had been his birthday a few weeks ago so we had a little joint party for the two birthday guys! They were equally enamored with the cake as us, huge hit all-around 🙂

Let me tell you about the cake. As you can see, there are three distinct layers – on the bottom is a rich, fudgy flourless chocolate cake. It is the only component of this dessert that is baked. Sitting atop the chocolate cake is a luscious dark chocolate mousse, and finally a sweet and smooth white chocolate mousse on top of that. Garnished with a few chocolate curls, this triple chocolate mousse cake is pretty much a work of art 🙂 I love how the layers all have the same thickness and slightly different colors to keep them distinct.

It might sound like a lot of work, but this cake really isn’t a huge project to make. I’d say it’s much easier than a traditional layer cake honestly. The only caveat – you will be washing the bowl of your stand mixer a million times, it’s re-used in each and every layer. It’s definitely a “dirty every bowl in the house” kind of recipe, but if ever there was a recipe worth doing it for, this is the one.

Triple Chocolate Mousse Cake
from Cook’s Illustrated, November/December 2009

Bottom Layer
6 tablespoons (3 oz) unsalted butter, cut into 6 pieces
7 oz bittersweet chocolate, finely chopped
3/4 teaspoon instant espresso powder
4 large eggs, at room temperature and separated
1 1/2 teaspoons vanilla extract
pinch salt
1/3 cup packed light brown sugar (2 1/2 oz)

Middle Layer
2 tablespoons Dutch-process cocoa powder
5 tablespoons hot water
7 oz bittersweet chocolate, finely chopped fine
1 1/2 cups cold heavy cream
1 tablespoon granulated sugar
1/8 teaspoon salt

Top Layer
1 tablespoon water
3/4 teaspoon powdered gelatin
6 oz white chocolate
1 1/2 cups cold heavy cream, divided
chocolate curls, to garnish

Preheat oven to 325 F. Spray a 9 1/2-inch springform pan (with at least 3-inch high sides) with nonstick cooking spray.

To make the bottom layer: Add the butter, chocolate, and espresso powder to a large heatproof bowl. Microwave in 30-second bursts at 50% power, stirring after each, until the mixture is melted and smooth. Set aside to cool for 5 minutes.

Meanwhile, in a stand mixer fitted with the whisk attachment, combine the egg whites and salt and beat on medium speed until frothy. Add half of the brown sugar (crumbling it with your fingers to make sure there aren’t any lumps) and mix until combined, then add the remaining brown sugar (again crumbling with your fingers) and increase the mixer to high speed. Beat until soft peaks form, scraping down the sides of the bowl once.

Whisk the vanilla and egg yolks into the slightly cooled chocolate mixture. Then, using a whisk, fold one third of the egg white mixture into the batter to lighten it. Switch to a rubber spatula and gently fold in the remaining egg whites until there aren’t any white streaks. Transfer the batter to the prepared pan and spread in an even layer.

Bake for about 15-18 minutes, or until the center of the cake is just set – it’ll be soft, but should spring back if gently pressed with your finger. Remove the pan to a wire rack and allow the cake to cool completely in the pan (it will collapse slightly as it cools). Leave the cake in the pan, even after it’s cool.

To make the middle layer: Whisk the cocoa powder and hot water together in a small bowl then set aside. Add the chocolate to a large heatproof bowl. Microwave in 30-second bursts at 50% power, stirring after each, until the mixture is melted and smooth. Set aside to cool for 3-5 minutes.

Meanwhile, add the heavy cream, sugar, and salt to the bowl of a stand mixer fitted with the whisk attachment. Beat on medium speed for about 30 seconds, or until the mixture begins to thicken. Bump the mixer up to high speed and beat until the mixture forms soft peaks, about 15-45 seconds longer.

Add the cocoa powder mixture to the slightly cooled melted chocolate and whisk until smooth. Then, using a whisk, fold one third of the whipped cream into the chocolate to lighten it. Switch to a rubber spatula and gently fold in the remaining whipped cream until there aren’t any white streaks. Transfer the mousse to the springform pan, spreading it into an even layer on top of the cooled cake. Gently hit the pan on the counter a few times to remove any large air bubbles (smooth the top of the mousse again if necessary). Use a damp paper towel to wipe any large drips of mousse off the inside of the pan (basically you’re just trying to keep the layers separate and distinct). Refrigerate the cake for at least 15 minutes while you make the top layer.

To make the top layer: Add the water to a small bowl, then sprinkle the gelatin over the top. Set aside for 5 minutes. Add the white chocolate to a medium heatproof bowl. Place 1/2 cup of the heavy cream in a small saucepan. Set over medium heat and bring to a simmer, then remove from the heat and whisk in the gelatin mixture until completely dissolved. Pour the cream over the white chocolate and whisk until the chocolate is melted and smooth. Set aside to cool for about 5 minutes, stirring every few minutes (the mixture will thicken as it cools).

Meanwhile, add the remaining cup of heavy cream to the bowl of a stand mixer fitted with the whisk attachment. Beat on medium speed for about 30 seconds, or until the mixture begins to thicken. Bump the mixer up to high speed and beat until the mixture forms soft peaks, about 15-45 seconds longer. Using a whisk, fold one third of the whipped cream into the chocolate to lighten it. Switch to a rubber spatula and gently fold in the remaining whipped cream until there aren’t any white streaks. Transfer the mousse to the springform pan, spreading it into an even layer on top of the chocolate mousse layer. Refrigerate the cake until set, at least 2 1/2 hours.

Right before serving, garnish the cake with chocolate curls, if using. Run a thin knife between the cake and the sides of the springform pan before removing the pan. For best results, cut slices of the cake using either a cheese wire or a hot knife (dip the knife in hot water and wipe dry).

Leftover cake will keep in the fridge for a few days.