Preheat the oven to 180’C (Fan 160’C) /Gas mark 4. Line a 12-hol muffin tin with 12 small paper cases.
Cream the butter and sugar together in a bowl until pale. Beat in the eggs a little at a time and stir in the vanilla essence.
Sift in the flour and cocoa powder, then using a large metal spoon, gently fold in, adding a little milk until the mixture is of a dropping consistency. Spoon the mixture into the paper cases until they are half full.
Bake in the oven for 10-12 minutes for the small cup cakes or 15-20 minutes for the larger cup cakes or until well risen and a skewer inserted into one of the cakes comes out clean. Set aside to cool for 10 minutes then remove from the tin to a cooling rack.
For the butter cream icing, beat the butter in a large bowl until soft. Add half the icing sugar and beat until smooth. Then add the remaining icing sugar with 1tbsp milk, adding more milk if necessary, until the mixture is smooth and creamy. Add food colouring of your choice and mix until well combined.
Either spread the icing onto the cupcakes in scary swirling motion or spoon the icing into a piping bag with a star nozzle and pipe the icing onto the cakes. Decorate with the sprinkles and 2D scary iced plagues.