Preheat the oven to 180 degrees and arrange 10-12 cupcake cases in a cupcake tin.
Cream the butter and sugar until light and fluffy. And gradually add the eggs making sure you don't curdle the mixture.
Sift in the flour and cocoa powder, and gentle stir it into the mixture, being careful not to knock any air out.
Evenly distribute the mixture between the cupcakes cases.
Bake for 15-17 minutes or until a skewer comes out clean.
Leave to cool over night.
For the buttercream, slightly melt the butter in the microwave and then add the icing sugar and vanilla essence to the bowl. Using an electric whisk, mix the ingredients together and add milk if the mixtures too thick.
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