This velvety Mary Berry Chocolate Mousse Cake is made with a light cocoa sponge base and topped with a thick, indulgent layer of whipped chocolate mousse. Ready after a few hours of chilling, it combines the richness of a truffle with the lightness of a classic cake. I love making this for dinner parties because it looks incredibly professional but requires zero decoration skills.

The Secret To Getting It Right

I learned the hard way that the type of chocolate you use for the mousse layer is absolutely critical. While I usually reach for 70% dark chocolate for baking, Mary Berry specifically recommends using plain chocolate with only 40% to 50% cocoa solids for this recipe. If the cocoa content is too high, the mousse becomes heavy and chalky rather than smooth and creamy.

Another surprise was the sponge method. Instead of creaming butter and sugar first, you mix cocoa powder with boiling water to create a paste before adding the other ingredients. This simple step blooms the cocoa, intensifying the chocolate flavour and ensuring the sponge stays incredibly moist even after sitting in the fridge.

Mary Berry Chocolate Mousse Cake Ingredients

For the Chocolate Sponge:
25g cocoa powder
3 tbsp boiling water
100g caster sugar
100g self-raising flour
1 tsp baking powder
2 large eggs
100g baking spread or softened butter
2 tbsp brandy (optional, for soaking)
For the Mousse Filling:
300g plain chocolate (39-50% cocoa solids)
450ml whipping cream
To Decorate:
Fresh raspberries or strawberries
Icing sugar, for dusting

How To Make Mary Berry Chocolate Mousse Cake

Prepare the Tin: Preheat your oven to 180°C (160°C fan/Gas 4). Grease a deep 20cm (8in) loose-bottomed tin and line the base and sides with baking parchment. Ensure the paper on the sides stands higher than the tin, as the mousse layer will be generous.
Mix the Sponge Base: Measure the cocoa powder into a large bowl and pour over the boiling water. Mix to a smooth paste. Add the sugar, flour, baking powder, eggs, and butter. Beat with an electric whisk until the mixture is smooth and combined.
Bake the Sponge: Pour the batter into the prepared tin and level the surface. Bake for 20-25 minutes until well-risen and shrinking slightly from the sides. A skewer inserted into the centre should come out clean.
Soak and Cool: While the cake is still hot, brush the brandy over the top if using. Leave the cake to cool completely inside the tin. Do not remove it, as the tin acts as the mould for the mousse.
Make the Mousse: Break the chocolate into pieces and melt gently in a heatproof bowl set over a pan of simmering water (don’t let the bowl touch the water). Stir until smooth, then set aside to cool until tepid.
Whip and Fold: Whip the cream until it holds soft peaks. Carefully fold the cooled melted chocolate into the cream until the mixture is smooth and no white streaks remain. Do not overbeat.
Assemble and Chill: Spoon the mousse over the cold sponge in the tin. Level the top with a palette knife. Cover and chill in the fridge for at least 4 hours, or preferably overnight, until firm.
Serve: Carefully remove the cake from the tin and peel away the parchment paper. Transfer to a serving plate, dust with icing sugar, and pile fresh berries on top.

Recipe Tips

Watch the Chocolate Percentage: Stick to chocolate with around 40-50% cocoa solids. Anything over 60% will make the mousse too stiff and bitter against the sweet cream.
Don’t Over-Whip the Cream: Stop whipping the cream when it reaches soft peaks (floppy), not stiff peaks. The mixture will thicken further as you fold in the chocolate, and over-whipped cream makes the mousse grainy.
Line the Sides High: The sponge is thin, but the mousse layer is deep. Make sure your baking parchment rises at least 2cm above the rim of the tin so the mousse stays contained.
Cool the Chocolate: If the melted chocolate is too hot when you add it to the cream, it will seize or melt the cream, destroying the airy texture. It should feel barely warm to the touch.

What To Serve With Mary Berry Chocolate Mousse Cake

This cake is extremely rich, so it needs something fresh to cut through the chocolate intensity. A generous pile of tart raspberries or strawberries is essential, not just for decoration but for flavour balance. For an extra treat, serve thin slices with a drizzle of single cream or a scoop of vanilla bean ice cream.

How To Store

Keep this cake refrigerated at all times when not serving, as the mousse is made of fresh cream. It will stay fresh in the fridge for up to 2 days. You can also freeze the finished cake (without fruit) for up to one month; defrost it overnight in the fridge before serving.

FAQs

Can I use milk chocolate instead?
You can, but the result will be much sweeter and the mousse might be slightly softer. If you use milk chocolate, omit the icing sugar dusting to keep the sweetness in check.
Can I make this without alcohol?
Yes, simply skip the brandy step. You can brush the sponge with a little orange juice or weak coffee if you want to keep the moisture, but it’s delicious without it too.
Why did my mousse seize?
This usually happens if the chocolate was too hot or if a drop of water got into the melting bowl. Ensure your equipment is bone dry and let the chocolate cool before folding.

Nutrition

Calories: 520 kcal
Total Fat: 42g
Saturated Fat: 25g
Cholesterol: 120mg
Sodium: 150mg
Total Carbohydrate: 35g
Protein: 6g