Preheat the oven to 200C/180C Fan/Gas 6. Line a 6 hole muffin tin.
In a large bowl, combine the dry ingredients (flour, cocoa powder, baking powder, sugar and a pinch of salt).
Make a well and add in the liquid ingredients (melted butter, milk, oil, peppermint extract and egg). Mix until just combined.
Add in the chopped chocolate/after eights and combine. Pour into the muffin liners, until about 2/3rds full. Bake 15-18 minutes, until a skewer inserted comes out clean. Let cool on a wire rack.
Make the icing by combining ingredients in a bowl/large mug. The icing should be really stiff. Add a teaspoon to each muffin before adding an After Eight!