Heat the milk with the cream and the cinnamon stick. Finely grate the chocolate and stir into the milk, stirring until it dissolves. Remove the cinnamon stick. Reserve 8 marshmallows, finely chop the rest and add to the chocolate. Stir until the marshmallows have dissolved. Whisk the hot chocolate with a hand blender and pour into cups. Add the reserved marshmallows as a garnish and dust with a little cinnamon. Put into a preheated oven (250°C with grill function) briefly to toast the marshmallows. Serve hot.