Wash your hands and tie back your hair. Preheat the oven to 200 C / gas 6. Put the paper cases in the bun trays and leave to one side.
In a bowl mix together butter and sugar until it is smooth and creamy. Gradually add the eggs until they are all beaten in. Add the cocoa powder and vanilla. Then gradually add the flour until all of the flour is gone. Add the milk gradually until it makes a smooth paste.
Gradually put the cake mixture into the bun cases. Make the bun cases half-full.
Now add the cake trays to the oven with the bun cases filled with the cake mixture. Leave the cup cakes in the oven for 15- 20 minutes.
You can tell they are ready once they are a light brown or if you stick a knife or fork into one of the cup cake and none of the cake mixture sticks to the knife or folk. Or you can tap one of your fingers onto one of the cakes and if it bounces back then it means it is done.
Once the cakes are done take them out of the oven and place the trays on a wire rack to cool completely before icing with your favourite icing recipe.