This chocolate mousse cake is decadent, rich, and surprisingly simple to prepare. It features a basic chocolate cake base topped with a light, airy chocolate mousse, all made with readily available ingredients.

Equipment

Cake tin with removable sides

Parchment paper

Cooking spray

Ingredients

1 cup (133g) all-purpose flour

¾ cup (150g) sugar

⅓ cup (30g) cocoa powder

1 tablespoon baking soda

½ tablespoon baking powder

¼ tablespoon salt

¼ cup (60ml) vegetable oil

1 large egg

½ cup (120ml) full-fat buttermilk

½ cup (120ml) hot water or hot coffee

2 cups (370g) chocolate chips or dark chocolate

2⅓ cups (560ml) heavy whipping cream

2 tablespoons powdered sugar

2 tablespoons vanilla extract

1 teaspoon instant coffee or espresso powder (optional)

Garnishes: raspberries or chopped chocolate

Instructions

Chocolate Cake:
Preheat your oven to 350°F (177°C). Grease the cake tin with cooking spray and line the base with parchment paper.
In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt. Add the vegetable oil, egg, vanilla extract, and buttermilk, mixing well. Gradually whisk in the hot water or coffee until the batter is smooth.
Pour the batter into the prepared pan and bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely before adding the mousse.

Chocolate Mousse:
Heat the heavy cream in a small saucepan over medium heat, stirring constantly until it starts to simmer. Pour the hot cream over the chocolate chips and whisk until the mixture is smooth. Let it cool to room temperature (about 25 minutes) before spreading it over the cake.

In a separate bowl, whip the remaining 1⅓ cups of heavy cream together with the powdered sugar, vanilla extract, and optional espresso powder. Start mixing on low speed, then increase to high and beat until stiff peaks form, about 4 minutes.

Once the melted chocolate mixture has cooled to room temperature, gently fold the whipped cream into it using a rubber spatula.

To serve:
Carefully remove the cooled cake layer from the pan. Trim the top with a knife to make it flat, then place it back into the parchment-lined tin.

Pour the chocolate mousse over the cake and spread it evenly with a spatula. Refrigerate for at least 6 hours or overnight to allow the mousse to set properly.

When ready, unmold the cake, garnish with raspberries or chopped chocolate, and enjoy. Store in the fridge for up to 5 days.

No buttermilk? Simply add two teaspoons of white vinegar to half a cup of whole milk to make a substitute.