Preheat oven to 180c / Gas 4
Sift the flour and cocoa into a large mixing bowl. Add the sugar and mix well to combine.
Put the butter in a pan and place over a low flame to melt. (You can also use the microwave to melt the butter)
Add the melted butter to the dry mixture and stir until the dough comes together into largish clumps. You may need to use your hands. This does not make a ball of dough, more like very uneven bread crumbs
Pour these into a 12 inch by 7 inch tin and press down with the back of a large metal spoon. Smooth as you press. The surface should appear shiny.
Using a pastry brush wet the surface of the biscuit mix. Don't flood it! A gentle caress should be enough
Put into the oven for 35 Minutes. When cooked, cool for 5 minutes before marking out the surface of the biscuit into portions. As the name suggests, you wont be able to do this once the concrete has set!
When completely cool, sprinkle a tiny amount of caster sugar on the surface.
Now you are ready to cut and serve!
