Pre heat oven 175oC. Grease and line a rectangular tray with baking paper. Beat butter, sugar, vanilla and egg in a bowl. Sift in flour, baking powder and cocoa and mix well. Stir in coconut.
Spread mix into tin and bake for 20-25 minutes or until firm. Remove from oven and spread with chocolate icing while still hot, then sprinkle with extra coconut. Cut into 12 slices when cold.