Place 16 mini silicone muffin cases on a baking sheet.
Sift the flour, cocoa powder and baking powder into a bowl. Stir in the sugar and chopped chocolate.
Beat the egg in a separate bowl and stir in the milk and melted butter. Add to the dry ingredients using a large metal spoon, stir the ingredients together until only just combined. Divide among the cases.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 15 minutes until risen and just firm. Serve warm or cold.