Preheat oven to 180°C and line 10 holes of a muffin pan with paper cases.
Sift the flour, sugar, cocoa, baking powder and 1/2 teaspoon of salt in a bowl.
Whisk buttermilk, egg, oil and vanilla in a separate bowl. Use a spatula to fold into dry ingredients until well combined.
Spoon batter into muffin cases. Bake for 25 minutes until a skewer inserted in the centre comes out clean. Cool slightly, then transfer to a rack to cool completely.
Meanwhile, for the icing, beat the sugar, butter and milk in a processor or electric mixer until soft. Add the food colouring a few drops at a time until you reach the desired colour.
Roll out black icing on a sheet of baking paper and use a small cutter to make decorative shapes (we used a cat, and pressed in cachous to make eyes).
Spread orange icing over cakes, then decorate with icing shapes.
