Preheat oven to 170 degrees C and butter a baking tin.
Stir the mascarpone into the melted chocolate. Beat the egg yolks with the sugar and add the cornflour. Stir into the chocolate mixture. Whisk the egg whites until stiff then fold into the batter.
Pour batter into the tin and bake about 25 minutes - the centre of the cake should still be soft. Remove from oven and let cool before unmolding. Before serving, sift over icing sugar and decorate with frui if desired.