Pour the red wine into a slow cooker pot and stir in the sugar.
Add the orange and lemon slices, cinnamon sticks, whole cloves, star anise, and 10-12 gratings of nutmeg.
Cook on low for 2-3 hours or until the wine is hot. Switch to the "keep warm" setting if your slow cooker has one so the wine stays warm during your event. Alternatively, simmer in a saucepan over low heat for 20-30 minutes.
Serve hot in heatproof glasses and garnish as desired. Enjoy!
Notes
You can add additional alcohol to the mulled wine if you wish such as Cointreau, Sloe Gin, or Ginger Wine. Add 100m/½ cup per 75cl bottle of wine at the end of cooking, just before serving.