Preheat the oven to 200C/180C Fan/Gas 6. Line a 6 hole muffin tin.
In a large bowl, combine the flour, baking powder, baking soda and sugar.
Make a well, and pour in the milk, egg, oil and butter (make sure it has cooled a little first). Add the chocolate chips and stir gently with a wooden spoon until just combined.
Scoop 1 tbsp batter evenly into each muffin hole. If using, add 1 square of milk chocolate to each, placed in the middle.
Scoop over the remaining batter evenly, ensuring that chocolate is covered. Bake for 15-18 Minutes until golden on top. Let cool on a wire rack.