Preheat oven to 190 C/ 170 C fan/ gas mark 5/ 375 F and line a 12 hole muffin tin with paper baking cases.
Sift the flour, bicarbonate of soda, sugars and chilli powder together in a large bowl.
Measure out the cocoa powder, water and butter into a small saucepan and heat gently over a low heat until the butter has melted and the ingredients are combined. Do not allow this to boil!
Measure out the milk and whisk the egg into it. Add the vanilla.
Add the melted chocolate mixture and the egg mixture to the dry ingredients and stir to combine well. The batter will be thin.
Spoon into the prepared baking cases and bake for 20 minutes until well rise and springy. A wooden skewer inserted into the centre of the cakes will come out clean when done. Transfer to a wire rack to cool completely.
Frost and sprinkle with as many (or as few!) crushed chilli flakes as you'd like.