1. Preheat the oven to 200°C. Grease and line a 25cm spring form tin with parchment paper.

2. In a clean bowl, whisk eggs and sugar until pale and thick. Sift the flour and cocoa together onto the mixture, then gently fold in, followed by the butter. Pour into the tin, ease to the edges, and bake for 8-10 minutes until risen and firm to the touch. Cool in the tin.

3. In the meantime, in a bain-marie, melt the chocolate over medium heat. Remove and set aside.

4. In a separate bowl beat the chestnut purée and egg yolks until smooth. Beat in the melted chocolate.

5. In another separate bowl, whisk the egg whites until stiff peaks form.

6. In a separate bowl, whip the remaining cream to medium peaks. Fold into the chocolate mixture, then carefully fold in the egg whites. Pour over the sponge base, then pour the chocolate mix on top. Level the surface and chill for at least 5 hours or until firm.

7. To serve, carefully remove from the tin, strip off the paper and slide onto a cake stand.
Dust heavily with cocoa.