1. Line the base of a 20cm springform tin and preheat oven to 180C.

2. Beat eggs and sugar with electric mixer until thick and pale. Fold in sifted flour and cocoa. Add melted butter and fold in gently until combined. Pour into prepared cake tin and bake for 15 minutes, or until a skewer inserted into the centre comes out clean. Leave to cool in tin for 10 minutes then remove from tin, remove baking paper and cool upside down.  

3. Meanwhile, allow cream to come to room temperature. Melt chocolate in a large bowl over simmering water. Set aside to cool slightly then add egg yolks and mix to combine, the mixture will become thick quickly. In a small saucepan, or in the microwave, heat 100mls of the cream until almost at boiling temperature, remove from heat. In a small dish, sprinkle gelatine over boiling water and stir to dissolve, then stir into the hot cream. Add cream to chocolate mixture and stir to combine.

4. In a separate bowl, beat egg whites in a stand mixer until soft peaks form. Add sugar 1 tablespoon at a time and continue beating until the sugar dissolves and the mixture becomes thick and glossy.

4. In a separate bowl, beat remaining cream and vanilla extract until stiff peaks form. Add whipped cream to chocolate mixture and fold to combine. Then fold through the egg whites in two batches until well combined.

5. Return cake to tin top side down and pour mousse mixture over cake. Smooth out top and refrigerate for at least 3 hours, preferably overnight.

If you have a little leftover mousse, pour into a small serving dish and refrigerate until set, it can be enjoyed on its own.

To remove cake from tin, gently warm the sides of the tin a little, with a hot towel or a hair dryer. Unclip and slide sides of tin away from the cake. Gently lift cake from base of tin using a flat spatula.

Dust cake with cocoa powder and serve with fresh berries and whipped cream on the side.