First of all mix the flour, sugar and cocoa together in a large bowl.

Melt the butter gently in a microwave or on the hob.

Add the melted butter and vanilla essence to the dry ingredients and beat in the egg.

Press the mixture, evenly into lightly greased tin.

Brush the tops with water and sprinkle with some additional sugar.

Oven bake at 170°C for at about 30 minutes.