Preheat your oven to 180 C / Gas 4. Place your cupcake cases in a cupcake tray.
Sift the flour, baking powder and salt into a large bowl and then add the sugar. Be sure they are thoroughly combined.
Place the margarine and chocolate in a bowl and place it over a saucepan of simmering water until they melt and combine, stirring occasionally. (You can also melt them directly in a saucepan, but you may risk burning the chocolate)
Set the chocolate mixture aside to cool for several minutes.
Beat the egg until slightly frothy, then add the vanilla and orange zest.
Add the egg mixture, chocolate mixture, and milk to the dry ingredients and stir until thoroughly combined. Be careful not to overmix.
Place 1 to 2 tablespoons of the mixture in each cupcake case.
Bake in your preheated oven for 30 minutes. Allow the muffins to cool for 15 to 20 minutes before serving.
You can decorate the top of your cupcakes with chocolate chips or chocolate sprinkles if you would like something a little less plain. This should be done before they go in the oven for best results. These are also great served with a dollop of whipped double cream.