Preheat the oven to 190 C / Gas 5. Line 2 (12-hole) muffin tins with paper cases.
In a bowl, sieve the flour and sugar together then add in the chocolate.
Melt the butter in a saucepan over a medium heat then pour into the flour and chocolate mixture. In a jug, whisk together the milk and egg then add the peppermint; pour into the flour mixture. Spoon the mixture into the prepared paper cases, filling only 3/4 full to ensure a good rise.
Bake in the preheated oven to 25 minutes, or until risen and a skewer inserted into the centre of a cupcake comes out clean. Remove from the oven and cool completely before decorating as desired.
You could just make it as a big cake and melt some more (of whichever) chocolate to drizzle on top.