Heat the oven to 170°C (150° fan) 325°F gas 3. Grease a 17cm|7" round cake tin.
Beat together the butter and chestnut spread in a mixing bowl until soft.
Beat in the egg yolks, cornflour and baking powder until well combined.
Whisk the egg whites until stiff, but not dry. Gradually fold into the chestnut mixture.
Pour into the tin and bake for 40-45 minutes. Cool in the tin on a wire rack.
To decorate: sift cocoa powder over the top and sides of the cake. Place strips of non-stick baking paper over the top of the cake. Sift over the icing sugar to form a chequerboard pattern, as in the photo.
Decorate with marrons glaces.