Heat the oven to 180C/160C fan/gas 4. Line a muffin tin with six muffin cases. Sieve the flour, cocoa and baking powder into a medium bowl. Mix together the egg, sugar, oil and milk together in a jug, then gradually pour into the dry ingredients (add chocolate chips now to make double chocolate muffins, if you like) and mix until combined.
Spoon the mixture evenly into the cake cases and bake for 20-25 mins until a skewer inserted into the middle comes out clean. Remove from the oven and leave to cool.
Meanwhile, gradually mix ½-1 tbsp water into the icing sugar until you have a loose consistency that's not too runny. Drizzle the icing over the muffins once cool.
How to serveThese are delicious warm. Simply leave them out of the oven to cool for a few mins before drizzling with the icing and digging in.