Chocolate Concrete

Chocolate concrete, remember this from school? with pink custard or mint custard? i make it a lot now.

200g plain flour
200g granulated sugar
100g butter
50g cocoa powder

mix the dry ingredients, then melt the butter and add that, then with your hands mix it into like a crumble mix, pop into greased tray and flatten down, press into tin so firm, into preheated oven for 20 mins gas mark 4, do not burn, take out, sprinkle with sugar and leave for bout 10 mins to firm up..