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Boxed Brownie Mousse Cake

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  • Author: Browned Butter Blondie
  • Prep Time: 60 mins
  • Cook Time: 25 mins
  • Total Time: 1 hour 25 mins
  • Yield: 1 1x
  • Category: Dessert


A silky smooth, decadent boxed brownie mousse cake is the ultimate chocolate lover’s dessert. A layer of rich chocolate mousse sandwiched between a thick, fudgy brownie and a cloud of freshly whipped cream. Pure chocolate heaven!



For the Brownie Layer

  • 1 boxed brownie mix

For the Chocolate Mousse Layer

  • 9 ounces (about 2 1/2 bars) dark chocolate, chopped {I use Valrhona 71% Cacao Dark Chocolate Bar}
  • 1/2 cup plus 2 TBSP heavy whipping cream
  • 4 egg yolks, room temperature
  • 1/4 cup plus 1 TBSP granulated sugar
  • 1/4 cup water
  • 2 egg whites, room temperature
  • 1/8 tsp salt

For the Whipped Cream Layer

  • 1 cup heavy whipping cream
  • 1 TBSP confectioner’s sugar


For the Brownie Layer

  1. Preheat oven to 350 degrees.
  2. Spray a 9 inch springform pan with non-stick cooking spray and line bottom and sides with parchment paper.
  3. Set aside.
  4. Mix a box of brownie mix according to package directions and spread into bottom of the prepared pan.
  5. Bake according to package directions, baking 5 minutes less than instructed.
  6. Remove pan from oven and allow brownies to cool.

For Chocolate Mousse Layer

  1. Whip heavy whipping cream in the stand of an electric mixer fitted with the whisk attachment until light and fluffy. Do not over mix.
  2. Place in refrigerator to keep cool.
  3. Over a double boiler on medium-low heat, melt chopped chocolate, stirring often until smooth and fully melted.
  4. Remove from heat.
  5. In a clean bowl in the stand of an electric mixer, whip egg yolks on high.
  6. Meanwhile, heat water and granulated sugar on high heat in a small saucepan.
  7. Once boiling, very slowly add the sugar/water mixture to the beaten egg yolks in the mixer and continue to beat on high speed.
  8. Mixture will thicken and cool and be pale yellow.
  9. Using large folding motions, mix the melted chocolate into the egg yolk mixture until combined.
  10. In a separate clean bowl of an electric mixer, whip egg whites until foamy but not dry.
  11. Quickly stir 1/3 of the egg white mixture into the chocolate mixture, incorporating completely.
  12. Gradually add the rest of the egg whites using large folding motions.
  13. Remove whipped cream from refrigerator and gently fold into the chocolate mixture until combined.
  14. Spread the mousse onto the top of the cooled brownie, using and offset spatula to level the brownie layer.
  15. Place pan in refrigerator.
  16. Mix 1 cup of heavy whipping cream and 1 TBSP confectioner’s sugar in the stand of an electric mixer with the whisk attachment until smooth but not completely set.
  17. Remove from mixer and continue to mix with a hand held whisk for 30 seconds until whipped and smooth.
  18. Remove mousse from refrigerator and spoon whipped cream on top of the mousse layer, again using a spatula to level the top.
  19. Refrigerate for 4 hours or overnight.
  20. Sprinkle top of cake with chocolate shavings or curls.
  21. Serve cold.


Left over cake can be stored tightly wrapped in refrigerator.
When baking boxed brownies, add 2 TBSP freshly brewed espresso instead of water for a richer, more chocolatey brownie.