Preheat the oven to 180°C/Gas Mark 4. Melt the butter. Turn off the heat and add the chocolate, then leave to cool.
Beat the eggs with the sugar until you get a clear mixture. Add the milk and melted chocolate.
Add the sifted flour, baking powder and cocoa and blend to combine. Add the chocolate chips, then pour into cupcake or muffin cases and bake for 25 minutes.