Preheat the oven to 150-160 degrees. Heat the milk, stir in the cocoa powder. Mix the hot cocoa with the rum and fill it into cups. Put the marshmallows on top and bake it for 15 minutes in the oven. Take the drinks out of the oven (attention of the very hot cup!).

Tip: For cinnamon winter taste put some cookies in each cup. The cookies will melt in the hot chocolate and give the drink a nice flavour. If you want, you can also melt the marshmallows with a Bunsen burner.