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Bite missing from a slice of chocolate cake with chocolate mousse.

Chocolate Cake with Chocolate Mousse

This chocolate mousse cake has four moist cake layers filled with a stabilized chocolate mousse that holds its shape and a glossy ganache drip.
5 from 1 vote
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Prep Time 30 minutes
Cook Time 30 minutes
chill time 1 hour
Total Time 2 hours
Course Dessert
Cuisine American
Servings 14 slices
Calories 639 kcal

Ingredients
 
 

For the cake:

  • 1 ¾ cups Granulated sugar
  • 2 teaspoon Vanilla extract
  • ½ teaspoon Kosher salt
  • 3 Eggs
  • ¾ cup Buttermilk
  • ½ cup Sour cream
  • ⅔ cup Cocoa powder Dutch processed
  • ⅔ cup Vegetable oil
  • ¾ cup Coffee Hot
  • 2 cups Flour AP, plain
  • 2 teaspoon Baking powder
  • ½ teaspoon Baking soda

For the chocolate mousse:

Melt:

  • 6 oz Dark chocolate
  • 10 oz Heavy cream

Whip:

  • 2 ½ cups Heavy cream
  • 1 teaspoon Vanilla extract
  • 3 tablespoon Cocoa powder
  • 4 tablespoon Powdered sugar

Gelatin:

  • 10 g Gelatin powder
  • 60 g Water

For the chocolate ganache:

  • 2.5 oz Dark chocolate
  • 2.5 oz Heavy cream

Instructions
 

Make the cake layers

  • Prep: Preheat your oven to 180°C (350°F). Line two 8-inch cake pans with parchment paper and spray with nonstick cooking spray.
  • Mix Wet Ingredients: In a large mixing bowl, whisk together eggs, buttermilk, oil, vanilla extract, salt, sugar, sour cream, and sifted cocoa powder until smooth.
  • Add Dry & Coffee: Sift in flour, baking powder, and baking soda. Whisk until almost combined, then pour in hot coffee. Mix gently until the batter is smooth and lump-free.
  • Bake & Cool: Divide batter evenly between the two prepared 8-inch pans (weigh with a kitchen scale for accuracy). Bake for 25 to 30 minutes, until a toothpick inserted into the center comes out clean. Cool completely.
  • Slice Layers: Once fully cooled, use a long serrated knife to slice each cake layer in half horizontally, yielding four even layers total.

Make the Stabilized Mousse

  • Bloom Gelatin: In a small bowl, combine cold water and gelatin powder. Let sit for 10 minutes to bloom.
  • Melt Chocolate: Melt chopped dark chocolate and ½ cup of heavy cream together in 15-second microwave bursts (or over a double boiler) until smooth and emulsified.
  • Whip Cream: In a separate chilled bowl, whip cold heavy cream, sifted cocoa powder, powdered sugar, and vanilla extract until soft peaks form.
  • Melt Gelatin & Combine: Microwave the bloomed gelatin in 5-second pulses until fully liquid (do not boil). Whisk the liquid gelatin into the melted chocolate mixture.
  • Fold Mousse: Fold ½ cup of whipped cream into the warm chocolate mixture to loosen it. Gently fold in the remaining whipped cream in two additions until smooth and streak-free.

Assemble & Apply Ganache

  • Stack & Fill: Place the first cake layer on a serving plate. Spread ¼ of the chocolate mousse evenly over the top. Repeat with the second and third cake layers.
  • Frost & Chill: Place the fourth cake layer on top and frost the top and sides of the entire cake with the remaining mousse. Chill in the fridge for 30 minutes to set.
  • Make Ganache: Heat heavy cream until simmering, pour over chopped dark chocolate, let sit undisturbed for 3 minutes, then whisk until smooth and glossy.
  • Drip & Decorate: Let ganache cool until slightly thickened, then pour over the chilled cake, nudging gently toward the edges with an offset spatula to create drips. Chill for another 15 minutes before serving.

Notes

  • Use a Digital Scale for Accuracy: For the best crumb and moisture balance, measure flour, cocoa powder, and sugar by weight in grams rather than volume.
  • Control Gelatin Temperature: Always sprinkle gelatin over cold water to hydrate evenly. When melting bloomed gelatin, pulse in 5-second intervals—never boil it, as high heat weakens its setting power.
  • Match Chocolate & Cream Temperatures: Ensure the melted chocolate-gelatin mixture is lukewarm (around 30–35°C / 85–95°F) before folding in whipped cream. If it's too hot, it will melt the cream; if too cold, the gelatin will freeze into tiny rubbery specks.
  • Choose Baking Bars Over Chocolate Chips: Use high-quality dark chocolate bars (60–70% cocoa) for both the mousse and ganache. Standard chocolate chips contain stabilizers that prevent them from melting smoothly.
  • Room Temperature Dairy & Eggs: Pull eggs, sour cream, and buttermilk out of the fridge 30–45 minutes before baking so they emulsify smoothly into the batter without curdling.
  • Chill Layers Before Slicing: Freshly baked cake layers crumble easily when cut. Wrap completely cooled layers in plastic wrap and chill in the fridge for 30 minutes before slicing horizontally with a long serrated knife.
  • Serving & Storage: Serve the cake chilled directly from the fridge for the cleanest slices. Cover any cut surfaces with plastic wrap to keep the sponge moist for up to 4 days.

Nutrition

Calories: 639kcalCarbohydrates: 55gProtein: 8gFat: 46gSaturated Fat: 23gPolyunsaturated Fat: 8gMonounsaturated Fat: 12gTrans Fat: 0.1gCholesterol: 118mgSodium: 236mgPotassium: 334mgFiber: 4gSugar: 32gVitamin A: 1127IUVitamin C: 0.5mgCalcium: 129mgIron: 4mg
Keyword Chocolate Cake with Chocolate Mousse
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