Mix all the ingredients in a bowl, adding the milk last and gradually stirring in with a spoon.
Add the mixture in even quantities to cake cases placed in the Pyrex Magic muffin tray, ensuring to leave a little space above the mixture to allow for rising. Or you can grease the muffin tray and add the mixture directly into the tray.
Bake for 20 minutes.
Check they are cooked through by inserting a metal skewer in to the centre of the muffin and ensuring that it comes out clean.
Mix together with a fork the butter, icing sugar and water until smooth (Add the water gradually until desired consistency reached.
Smooth on to the muffins.
Grate the dark chocolate on to the cupcakes until covered.