Cream the butter and sugar together using a hand held mixer for around 5 minutes or until the butter and sugar becomes light and fluffy. In batches, add the self- raising flour, the tea spoon of baking powder with one egg at a time to the butter and sugar mixture and mix well until everything is blended. Once the flour and eggs have been blended, add the coco to the mixture and mix well. Add the milk to loosen the mixture. Divide the mixture in 12 muffin cases – I like to add a tablespoon at a time to each case so that the cupcakes are fairly even in size and appearance. Bake the cupcakes for 15-20 minutes or until risen, golden brown. If you have one, test with a metal skewer to make sure the cupcakes are cooked and no mixture is on the skewer.