To melt the chocolate, heat a saucepan of water over medium heat until the water simmers (just below a boil). Break the chocolate into a heat proof bowl and set it over the pan. Heat and stir until the chocolate is melted, then remove the bowl from the heat.
Sift the flour, baking powder and cinnamon into the bowl of chocolate. Mix it all together. Add the sugar and the chocolate chips and mix again.
In another bowl, mix together the milk, oil, vanilla and beaten egg. Add this mixture to the dry ingredients and stir just until it is blended together.
Spoon the batter into the prepared muffin cups.
Bake for 15-20 minutes in the preheated oven, until the muffins have risen and are firm to the touch. Check for doneness by inserting a toothpick into a few of the muffins. They are done when there is no batter clinging to the toothpick when you remove it.
Cool muffins in the pan for 5 minutes, then place them on a wire rack to cool completely.