Preheat oven to 180°C/160°C (fan)/Gas Mark 4/350°F
Line baking tray or tin with greaseproof paper or grease with a little butter
Cream the butter and sugar together in a bowl until smooth, sift the flour and cocoa powder into the bowl and mix together. This step can be done in a bowl or food processor.
Transfer the dough to a tin, or if you are making cookies, seperate the dough into roughly 12 balls and then use the back of a spoon or knife to press it down. If the dough feels a bit sticky and soft (this can happen if it is over handled) you can wrap it in some cling film and leave it in the fridge for about 30 minutes - 1 hour until is hardens up a little bit.
Cook in the preheated oven for 10 to 15 minutes for cookies or 25 minutes if you are cooking the dough as one in a baking tin.
Notes
note 1: you can use chocolate chips, or, if you don't have any you can use a finely chopped up chocolate bar.