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A close-up shot showing the light, fluffy texture and tiny air bubbles of a rich, dark brown chocolate mousse cake filling. (Chocolate Mousse Cake Filling)

The Ultimate Chocolate Mousse Cake Filling Recipe

The perfect Chocolate Mousse Cake Filling recipe! Learn how to make a light, aerated, and stable chocolate mousse paired with an incredibly moist dark chocolate sponge cake for the ultimate layer cake dessert.
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Prep Time 40 minutes
Cook Time 35 minutes
Total Time 1 hour 15 minutes
Servings: 12 slices
Course: Dessert
Cuisine: American, French
Calories: 550
Ingredients Equipment Method Notes

Ingredients
  

For the Moist Dark Chocolate Sponge Cake
  • 1 1/2 cups (180g) all-purpose flour
  • 1 1/2 cups (300g) granulated sugar
  • 3/4 cup (75g) dark cocoa powder
  • 1 1/2 tsp baking soda
  • 3/4 tsp baking powder
  • 3/4 tsp fine sea salt
  • 2 large eggs
  • 3/4 cup (180ml) buttermilk
  • 1/2 cup (120ml) neutral oil
  • 2 tsp vanilla extract
  • 3/4 cup (180ml) boiling water or hot coffee
For the Aerated Chocolate Mousse
  • 8 ounces (225g) high-quality dark chocolate (70% cacao) finely chopped
  • 2 cups (480ml) heavy whipping cream divided
  • 1 1/2 tsp unflavored gelatin
  • 3 tbsp (45ml) cold water
  • 1/4 cup (50g) granulated sugar
  • 1 tsp vanilla extract

Equipment

  • 1 Stand mixer or hand mixer
  • 2 8-inch (20cm) Round Cake Pans
  • 1 Offset spatula

Method
 

Baking the Moist Dark Chocolate Sponge
  1. Preheat oven to 350°F (175°C). Grease, flour, and line two 8-inch round cake pans with parchment paper.
  2. In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt.
  3. In a separate bowl, combine eggs, buttermilk, oil, and vanilla. Pour the wet ingredients into the dry and mix on low until just combined.
  4. Carefully mix in the boiling water/hot coffee until the batter is smooth and thin. Pour evenly into the prepared pans.
  5. Bake for 30-35 minutes, or until a skewer comes out clean. Cool in pans for 15 minutes before inverting onto a wire rack to cool completely.
Assembling the Aerated Chocolate Mousse Filling
  1. In a small bowl, sprinkle gelatin over cold water and let bloom for 5-10 minutes.
  2. Place chopped chocolate in a heatproof bowl. Heat 1/2 cup (120ml) of heavy cream until simmering, then pour over chocolate. Let sit for 2-3 minutes, then stir until smooth.
  3. Microwave the bloomed gelatin for 5-10 seconds to liquefy it, then whisk it into the warm chocolate ganache.
  4. In a separate cold bowl, whip the remaining 1 1/2 cups (360ml) of heavy cream with sugar and vanilla until stiff peaks form.
  5. Gently fold one-third of the whipped cream into the chocolate base to lighten it. Fold in the remaining whipped cream until no streaks remain.
The Final Assembly
  1. Place one cooled sponge layer on a serving plate. Top with a thick layer of the chocolate mousse and spread evenly with an offset spatula.
  2. Place the second sponge layer on top. Chill the assembled cake for at least 2 hours to allow the mousse to set before serving.

Notes

Don't Overheat Your Chocolate: When melting the chocolate with the hot cream, let it sit first. Stirring it too early when it's too hot can cause it to seize.
Whip Cream When Cold: For the best volume, make sure your heavy cream, bowl, and whisk are as cold as possible.
The Art of Folding: Use a large spatula and a gentle hand. Cut down through the middle of the bowl, scrape along the bottom, and bring the mixture up and over. This preserves those precious air bubbles.
Patience is Key: Allow the cake and the mousse to chill properly. Chilling ensures clean slices and allows the flavors to meld together beautifully.