Introduction

This Dark Chocolate Mousse Cake is a decadent treat combining rich chocolate layers with a smooth, airy mousse. Perfect for special occasions or any time you crave an indulgent dessert.

Ingredients

1 and 3/4 cups (219g) all-purpose flour (spooned & leveled)
1 and 3/4 cups (350g) granulated sugar

3/4 cup (64g) unsweetened natural cocoa powder
2 teaspoons espresso powder (optional)

2 teaspoons baking soda
1 teaspoon baking powder

1 teaspoon salt
3/4 cup (180g) full-fat sour cream, at room temperature
1/2 cup (113g/120ml) vegetable oil

2 large eggs, at room temperature
1/2 cup (120g/ml) buttermilk, at room temperature
2 teaspoons pure vanilla extract

1/2 cup (120g/ml) hot water or black coffee
1 cup (170g) semi-sweet mini chocolate chips tossed in 1 Tbsp flour (optional)
1/2 cup (120g/ml) hot water

1/4 cup (21g) unsweetened natural or Dutch-process cocoa powder
8 ounces (226g) quality semi-sweet chocolate, finely chopped
2 cups (480g/ml) heavy cream, cold

2 Tablespoons confectioners’ sugar
1/2 teaspoon pure vanilla extract
8 ounces (226g) quality semi-sweet chocolate, finely chopped (for ganache)

1 cup (240g/ml) heavy cream (for ganache)
Optional garnish: fresh berries and/or chocolate shavings

Instructions

Step 1: Preheat the oven to 350°F (177°C). Grease four 8-inch or 9-inch cake pans, line with parchment paper rounds, then grease the parchment paper.

Step 2: In a large bowl, whisk together flour, sugar, cocoa powder, espresso powder, baking soda, baking powder, and salt. Set aside.
Step 3: In another bowl, mix sour cream, vegetable oil, and eggs on medium-high speed until combined. Add buttermilk and vanilla extract and mix again.
Step 4: Pour the dry ingredients into the wet mixture, add hot water or coffee, and whisk on low speed until just combined. Fold in floured mini chocolate chips if using.

Step 5: Divide the batter evenly among the prepared pans. Bake for 19–23 minutes or until a toothpick inserted in the center comes out clean. Cool in pans for 1 hour, then remove and cool completely on a rack.
Step 6: For the mousse, whisk hot water and cocoa powder until smooth. Melt 8 ounces chopped semi-sweet chocolate using a double boiler or microwave in 20-second increments, stirring until smooth.
Step 7: Stir cocoa mixture into melted chocolate until thick and smooth. In a large bowl, whip 2 cups cold heavy cream, confectioners’ sugar, and vanilla extract until medium peaks form. Fold in chocolate mixture gently. Cover and refrigerate at least 2 hours.

Step 8: Level cake layers if needed. Place one cake layer on a serving plate, spread about 1.5 cups mousse evenly on top. Repeat with remaining layers, finishing with mousse covering the sides as a crumb coat. Smooth sides with a bench scraper and refrigerate for 1 to 4 hours.
Step 9: Prepare ganache by heating 1 cup heavy cream until just simmering. Pour over 8 ounces chopped semi-sweet chocolate and let sit 2–3 minutes. Stir until smooth and refrigerate 30 minutes to 1 hour to thicken.
Step 10: Spoon or pour thickened ganache over chilled cake, smoothing top and sides. Garnish with fresh berries or chocolate shavings if desired. Serve immediately or chill up to 4–6 hours before serving.

Tips & Variations

Use espresso powder in the batter to enhance the chocolate flavor without adding a coffee taste.
For a dairy-free option, substitute coconut cream for heavy cream and a plant-based sour cream alternative.
Flouring the mini chocolate chips helps prevent them from sinking to the bottom of the cakes.

Ensure eggs and dairy are at room temperature for a smoother batter and better rise.
For easier layering, chill the mousse until firm but still spreadable.

Storage

Store leftover cake tightly covered in the refrigerator for up to 5 days. For best texture, bring the cake to room temperature before serving. If needed, you can gently warm slices in a microwave for 10–15 seconds.

How to Serve

Serve this delicious recipe with your favorite sides.

FAQs

Can I make this cake ahead of time?

Yes, you can prepare the cake layers and mousse up to two days in advance. Assemble and chill the cake before adding ganache on the day of serving for the freshest results.

What if I don’t have espresso powder?

You can omit espresso powder without affecting the cake’s texture; it simply enhances the chocolate flavor. Using strong brewed coffee instead of water in the batter is another way to deepen the flavor.