Preheat oven to 165 degrees and place cupcake cases into cupcake tin.
Beat together butter and sugar until well combined
Add flour, cocoa powder, baking powder, eggs and cream liquor.
Spoon the mixture between your 12 cupcake cases. Bake in the oven for 20 minutes.
Leave to cool in tin.
In the meantime, prepare the buttercream icing.
Beat better in mixer until smooth, add the sugar in 1/3 measurements and beat well. Slowly add the cream liquor. You may not need it all! place the buttercream in a piping bag with a star nozzle. Pipe icing onto cooled cupcakes and enjoy within 2 days.