Cooking Steps

Grind the chestnuts to a mealy paste. Transfer to a large mixing bowl and sieve in the cocoa powder. Stir.
Melt the butter, honey and chocolate together until smooth. Stir in the vanilla extract.
Add the egg yolks to the melted chocolate mixture, one at a time, beating them in to turn the mix glossy.
Pour the chocolate mix into the chestnut mix and stir until combined.
Beat the egg whites until they form stiff peaks. Fold into the chocolate batter and then spoon into a greased or lined 8in x 8in baking tray. Bake at 350 for 12-15 minutes until firm then let cool before cutting and serving.