Melt the butter in a pan. Place flour, sugar and cocoa powder in a bowl and mix together.

Add the melted butter and the egg to the dry ingredients and combine.

Grease a baking tray (Aprrox 1 inch in depth). Put the mixture into the tray and pat it down until it is level.

Bake for 15 minutes and if you would like it crunchier then after 15 minutes, leave it in the over with the gas down for around 15-30 minutes. Sprinkle with caster sugar whilst hot.