Tuxedo Chocolate Mousse Cake
"Three layers of chocolate. Two kinds of mousse. One cake to rule them all."
Costco Copycat — This is a homemade version of the Costco Bakery item. See it in store →
The Game Plan
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Preheat oven to 350°F (175°C). Grease and line a 9-inch springform pan with parchment paper.
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**Make the cake layer:** Melt butter and 1 cup chocolate chips together in a saucepan over low heat, stirring constantly. Remove from heat and let cool 5 minutes.
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Whisk in 1/2 cup sugar, 3 egg yolks, and vanilla until smooth. Sift in flour and cocoa powder and fold until just combined.
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In a clean, dry bowl, whip 3 egg whites to stiff peaks. Fold into the chocolate batter in three additions — be gentle, you want to keep the air in.
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Pour into the prepared pan and bake 20-25 minutes until a toothpick comes out with moist crumbs. Cool completely in the pan. Don't even think about assembling until this is truly cold.
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**Make the dark chocolate mousse:** Melt remaining 1 cup chocolate chips and let cool until warm but not hot (if it's too hot, it'll melt the cream). Whip 2 cups heavy cream to soft peaks. Fold the melted chocolate into the whipped cream in three additions until no streaks remain.
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**Make the white chocolate mousse:** Melt white chocolate gently — microwave in 20-second bursts, stirring between each. Let cool to room temperature. Whip 2 cups heavy cream with 1/4 cup sugar to soft peaks. Fold in the melted white chocolate until smooth.
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**Assemble:** Place the cooled cake back in the springform pan. Spread the dark chocolate mousse evenly on top, smoothing with an offset spatula. Then spread the white chocolate mousse on top of that.
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Cover with plastic wrap and refrigerate at least 4 hours, or overnight for the best texture. Patience is a virtue and also the difference between mousse and chocolate soup.
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When ready to serve, run a warm knife around the inside of the springform ring before releasing. Whip remaining 1 cup cream with a tablespoon of sugar and spread or pipe on top.
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Dust with cocoa powder, powdered sugar, or chocolate shavings. For extra flair, press chocolate curls around the sides.
