Preheat the oven to 170°C and line a 12-hole muffin tray with paper cases.
Beat the butter and sugar together until light and creamy.
Gradually beat in the eggs until well combined.
Sift in the flour and cocoa powder and mix until combined.
Fold in the milk, melted chocolate, and liqueur if using.
Spoon the mixture into cases and bake for 20-25 minutes until risen.
Cool the cakes completely on a cooling rack.
Heat chocolate and cream over low heat until melted then whisk until smooth.
Spread icing over cupcakes and put the remainder in a piping bag.
Decorate with chocolate buttons for noses and crisp-coated chocolates on top.
Add marshmallow slices for eyes and use writing icing for pupils.
Stick on pretzels to form the reindeer ears.