Combine butter, chocolate, coffee and whisky in a bowl. Melt over steam.
Add sugar. Stir until smooth.
Stir in flour, baking powder and cocoa followed by eggs.
Pour into a greased and lined square tin and bake at 170 degrees C for 1 1/4 hours.
Cool slightly before turning out.
Serve dusted with icing sugar or topped with peppermint icing.
For peppermint icing:
Mix all the ingredients together until smooth.
Spread over the cake.