This chocolate mousse cake has four moist cake layers filled with a stabilized chocolate mousse that holds its shape and a glossy ganache drip.
While standard mousse cakes tend to slide apart at room temperature, this recipe relies on a touch of gelatin to create a stabilized chocolate mousse filling.
It holds its structure, stays firm when sliced, and delivers clean, bakery-style layers every time.
Moist chocolate cake layers are enriched with sour cream and buttermilk, while hot coffee blooms the cocoa powder for a deep chocolate taste that stays fresh for days.
One reader, Riley, commented: “This cake is so insanely good ★★★★★”
For more delicious chocolate cake recipes, check out my chocolate cake with chocolate cream cheese frosting, chocolate Brooklyn blackout cake, and chocolate mayonnaise cake.
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Why You’ll Love This Recipe
- Stabilized Mousse Filling: A touch of gelatin stabilizes the chocolate mousse so it holds tall layers without bulging, collapsing, or sliding.
- Ultra-Moist Crumb: Oil, sour cream, buttermilk, and hot coffee keep the chocolate sponge tender and moist for days.
- Four-Layer Impact: Slicing two baked 8-inch cake layers in half creates an impressive four-layer cake with half the baking hassle.
- Decadent Ganache Drip: A poured dark chocolate ganache finish adds double chocolate flavor and a professional bakery look.
Ingredients
Before starting, measure and prepare your ingredients so the baking process goes smoothly. You can find the exact measurements in the recipe card at the bottom of this post.
For the chocolate cake
All-Purpose Flour: Provides the core structure for the cake layers. Cake flour also works for an even softer crumb.
Dutch Process Cocoa Powder: Gives the sponge a dark chocolate color and smooth taste. Natural cocoa powder works as a swap.
Baking Powder & Baking Soda: Dual leaveners that help the batter rise into tall, fluffy layers.
Granulated Sugar: Sweetens the cake and retains moisture in the crumb.
Vegetable Oil: Ensures the cake layers stay ultra-moist even when chilled. Canola oil works as an equal swap.
Sour Cream: Adds richness and subtle acidity to balance the cocoa. Full-fat Greek yogurt works as a swap.
Eggs: Large and at room temperature so they emulsify smoothly into the batter.
Buttermilk: Adds moisture and activates the baking soda for a tender crumb.
Hot Coffee: Blooms the cocoa powder to deepen the chocolate flavor without leaving a coffee taste behind.
Vanilla Extract & Kosher Salt: Enhances the warm cocoa notes and balances the sweetness.
For the chocolate mousse
Dark Chocolate (60–70%): Provides the main flavor base. Use high-quality baking bars or chips.
Heavy Cream: Kept cold for whipping to create light, airy volume.
Unsweetened Cocoa Powder: Sifted into the cream for extra chocolate depth and rich color.
Powdered Sugar: Lightly sweetens the mousse without creating a grainy texture.
Gelatin Powder: Dissolved in cold water and melted to set the mousse for clean, sliceable layers.
Cold Water: Used to bloom the gelatin powder before melting.
Vanilla Extract: Enhances the smooth chocolate flavor.
The chocolate ganache drip
Dark Chocolate: Use high-quality chopped dark chocolate for a glossy drip.
Heavy Cream: Heated and poured over the chocolate to create a smooth, pourable ganache.
Step-by-Step Instructions
Bake 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 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.
Expert Tips
- Bloom Gelatin in Cold Water: Always sprinkle gelatin over cold water, not warm water, to ensure it hydrates evenly without forming rubbery lumps.
- Fold Gently: Use a silicone spatula to fold the whipped cream into the chocolate mixture in gentle circular motions so you don't deflate the trapped air.
- Chill Before Dripping: Always refrigerate the frosted mousse cake before pouring warm ganache. A cold surface helps the ganache set quickly into controlled drips.
- Slice with Warm Water: Dip a sharp knife into hot water, wipe dry, and make clean cuts. Repeat between every slice for picture-perfect bakery slices.
Troubleshooting
Why is my chocolate mousse runny or soft?
This happens if the whipped cream was under-whipped before folding or if the melted chocolate mixture was too hot when combined with the cream, melting the fat structure. Ensure the chocolate is lukewarm and the gelatin is completely dissolved.
Why did my ganache drip run all the way down to the serving plate?
If the ganache is too warm, it stays too thin and flows too fast. Let the ganache cool at room temperature until it reaches a warm-honey consistency, and ensure the cake is thoroughly chilled.
Why did my cake layers crumble when slicing in half?
Warm cake layers crumble easily. Chill the baked layers in the fridge for 30 to 45 minutes before slicing horizontally with a long serrated knife.
Frequently Asked Questions
While un-stabilized mousse works for small cups, gelatin is necessary for tall layer cakes. It keeps the mousse firm enough to support four cake layers and stay sliceable at room temperature.
Yes, but keep in mind that milk chocolate contains more sugar and cocoa butter. Reduce the powdered sugar in the mousse by half so the filling isn't overly sweet.
You can assemble the cake up to 24 hours in advance and keep it chilled in the fridge. Add the ganache drip on the day you plan to serve.
Storing
Store the cake in a cake keeper or airtight container in the refrigerator for up to 4 days. Serve chilled or let sit at room temperature for 15 minutes before slicing.
Freezing
You can freeze the assembled cake (or individual slices) in an airtight container for up to 3 months.
If freezing individual slices, wrap them tightly in plastic wrap before placing them in a freezer bag. Thaw in the fridge overnight before serving.
Make It Ahead Of Time
Bake Layers: Bake up to 2 days ahead, wrap tightly in plastic wrap, and store at room temperature or in the fridge.
Prep Mousse & Assemble: Assemble the four cake layers with mousse up to 24 hours early and chill.
Make Ganache: Prepare the ganache drip on the day of serving for the glossiest finish.
Substitutions
Dairy Free: Swap buttermilk with almond milk + 1 tablespoon lemon juice, and replace heavy cream in both mousse and ganache with chilled full-fat canned coconut cream or plant-based heavy whipping cream.
Egg Free: Replace the 2 eggs with ⅔ cup unsweetened applesauce.
Gluten Free: Swap all-purpose flour 1:1 with a measure-for-measure gluten-free baking flour blend containing xanthan gum.
Variations
Mocha Mousse Cake: Add 1 teaspoon of instant espresso powder to the chocolate mousse for a warm coffee flavor note.
Berry Mousse Layer: Add a layer of fresh raspberries or sliced strawberries over the mousse between each cake layer.
Chocolate Hazelnut: Spread a thin layer of warmed Nutella over each cake layer before topping with chocolate mousse.
Serving Tips
Serve chilled. The mousse holds its shape best cold. Garnish with fresh berries, chocolate curls, or a dusting of cocoa powder.
How to Scale This Recipe for Different Pans
Multiply all ingredient quantities in the recipe card by the percentage listed below for your target pan setup:
- Two 9-Inch Pans: Multiply the entire recipe by 130% (1.3). Use 3 large eggs. Bake at 175°C (350°F) for 28 to 32 minutes.
- 9x13 Inch Sheet Pan: Keep the recipe at 100%. Bake at 175°C (350°F) for 32 to 36 minutes (no slicing needed—top directly with mousse and ganache).
- Two 6-Inch Pans: Multiply the entire recipe by 60% (0.6). Use 1 large egg + 1 egg yolk. Bake at 175°C (350°F) for 24 to 28 minutes.
- Three 8-Inch Pans: Keep the recipe at 100% (bake 3 separate layers without slicing them horizontally). Bake at 175°C (350°F) for 22 to 25 minutes.
Equipment
- Mixing bowl
- Whisk
- 8-inch cake pans
- Rubber spatula
- Pastry bag
- Cake strips
- Electric hand mixer
- Kitchen scale
More cake recipes
Strawberry Lemon Cake- Soft strawberry lemon cake topped with strawberry cream cheese frosting and strawberry compote.
Pecan Upside Down Cake- Soft cinnamon-spiced cake topped with a rich caramel pecan glaze.
Fraisier Cake- Classic French strawberry cake made with génoise sponge, strawberry syrup, and diplomat cream.
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📖 Recipe
Chocolate Cake with Chocolate Mousse
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.
Riley says
This cake is so insanely good