Preheat the oven to 180'C.
Sift the baking powder and the flour.
Soften the butter to room temperature and place in the bowl of an electric whisk with the sugar and red food colouring. Using the paddle attachment beat until creamy whilst scraping the sides. Leave the machine running and add one egg at a time. Gently fold in the flour and the cocoa powder, divide into six cupcake cases and bake in the oven for about 15 to 18 minutes.
Check with a skewer whether the centre is cooked. Remove from the baking tray and allow to cool before doing any piping.
For the icing:
Allow the butter to come to room temperature. Beat the icing sugar with lemon zest and butter until creamy. Place in a piping bag with a nozzle and pipe the desired design on top of the cakes.
«You could substitute the lemon with lime or orange in the frosting.»