Heat the red wine adding cloves, star anise, sugar, and cinnamon sticks in a large pot. Make sure it does not boil. Stir well to dissolve the sugar.
Now add the orange slices.
Let it steep for about 10 minutes on very low heat to allow the holiday flavors to develop beautifully.
Rinse the glasses with hot water before serving. Strain the finished mulled wine into the glasses. If desired, add a splash of rum afterward.
Notes
Do not bring the wine to a boil; it should only be heated. Otherwise, the alcohol will evaporate too much. Add rum, amaretto, or other spirits only at the end into the mugs.