Make your syrup base: Add your orange juice and sugar to a large saucepan to a boil and stir until the sugar is completely dissolved.
Add your citrus and spices: Add your orange peel and then stir in your whole spices of cinnamon sticks, cloves, and star anise. Simmer on low for 1-3 minutes or until the mixture is thick and syrupy.
Pour in your wine: Pour your bottle of wine into the pot and let it cook at a very gentle low simmer for at least 20 minutes. You can cook your Glühwein up to 2 hours at this low heat to really let the flavors meld, but place a lid on the pot if cooking for longer than 20 minutes.
Pour and enjoy! When ready to serve, strain your Glühwein into your glasses and add a shot of brandy, bourbon, or rum if desired.