Rinse the orange or/and lemon with hot water. Peel them, if you are not using organic fruit. Cut into slices.
Heat up a store-bought red mulled wine to maxium 80° Celcius (176°F). If you made your own red mulled wine, make sure that it doesn't have more than 45°C (113°F). Otherwise, it will turn bitter. Fill the mug with mulled wine.
Place the sugarloaf on metal grate mounted on top of the Feuerzangenbowle mug.
Soak it carefully with rum and set alight.
Enjoy the view of the sugarloaf carmelizing and dropping into the mug.
Soak the metal grate into the mulled wine and enjoy your drink!