Preheat the oven to 180'C.
Put the chocolate and the butter into a heat proof bowl and melt over a sauce pan of simmering water.
Whisk together the egg, milk, sugar and yogurt. Combine the flour and the baking powder and then slowly fold the dry ingredients into the egg mixture. Add the melted chocolate to the mixture, combine well and then spoon the mixture into individual muffin moulds.
Bake in the oven for 10 to 15 minutes.
Leave on top of a wire rack to cool before serving.
«Check if the muffins are cooked by inserting a skewer into the centre. If it comes out clean then they are done. »