Preheat your oven to 180 C (170 C fan) and line a 12 hole muffin tin with large American size cupcake/muffin cases.
Cream butter and sugar together until light and fluffy. Add the egg, one at a time, with a spoonful of flour so it doesn't curdle.
Sift in the remaining flour and bicarbonate of soda and combine well.
Divide the mixture into two equal portions in separate bowls.
Add the cocoa powder to one half, and the peanut flour to the other half. Add a tablespoonful of milk to each bowl and stir until combined. It should be a soft, dropping consistency.
Drop small spoonfuls of each flavoured batter into the cupcake cases. Using a knife or skewer, swirl the batter together slightly to make a marbled cupcake.
Bake for 20-25 minutes, until springy and a skewer inserted comes out clean. Transfer to a wire rack to cool completely.
To make the frosting, blend the butter and icing sugar together until thoroughly combined.
Divide the mixture into two bowls, and add the cocoa powder to one bowl, and the peanut flour to the other. Add 1 tbsp milk to each bowl and combine well.
To pipe the swirled frosting you can either spoon each flavoured frosting into separate sides of a large piping bag, or use two small plastic disposable ones inserted into a third bag into which the medium star piping nozzle is fitted.
Frost and decorate with mini marshmallows!
Mum of three, daydream adventurer, OU Life Sciences graduate, occasional crafter, ex-pat Canadian & quite possibly Britain's most northerly food blogger.