Mix the butter and sugar in a bowl, then seperate the eggs and leave the whites to one side. Next add the egg yolk, self raising flour, cocoa powder and milk. Once this mixture is smooth and creamy, whisk the eggs whites until you get stiff peaks.
After dividing the mixture into the cupcake cases they need to bake for approximately 13-14 minutes.
Leave the cupcakes to cool for a couple of minutes before moving onto a wire rack. Forgot about the cupcakes for around 30 minutes before making the buttercream topping.
Simply put the butter, sugar, colouring and vanilla essence into a bowl and mix with an electric whisk.
Finally put the buttercream on top of the cupcakes and add the Cadbury's chocolate buttons for decoration.