Preheat the oven to 180°C (Electric oven | Electric fan oven 160°C | Gas Mark 4) and place 12 paper cases into a muffin tin.
Using an electric whisk, food processor or wooden spoon, beat the butter or margarine, sugar and cocoa powder until very light and fluffy.
Add the eggs one at a time, beating each one in well before adding the next.
Carefully fold in the flour (and baking powder if using).
Melt the chocolate and fold in to the mixture. Then thin the mixture with the milk.
Alternatively, you can mix the ingredients together using a food processor. Use the pulse button to mix together in between adding the ingredients in the order above.
Bake in the oven for 10 - 20 minutes. After 10 minutes, check to see if the chocolate cupcakes are ready by inserting a cocktail stick into one of the cupcakes. If it comes out dry then the cupcakes are done. If not, then back in the oven for a few minutes more. Don't overcook the chocolate cupcakes otherwise they will dry out. Lift the cupcakes out of the muffin tin and leave to cool on a wire rack.
Make the dark chocolate icing
Place the dark chocolate and butter in the microwave until just melted - a minute should do.
Using an electric whisk, food processor or wooden spoon, beat the mixture until combined.
When the cakes are cool, drizzle some chocolate icing mixture over the top of each cupcake. These chocolate cupcakes are best eaten on the day they are made.