Add wine, orange juice, cranberries, and sugar to a 3-quart or larger Crock Pot. Stir to help sugar begin to dissolve.
Wash orange thoroughly and stud the orange with the cloves - just stick the cloves directly into the peel, pointy end first. I like to poke it all over with a toothpick first to make holes for the cloves.
Add the clove-studded orange and the cinnamon sticks to the wine.
Cook on low for 2 - 3 hours, or until the berries are tender. You can cook it for an hour or two longer if you wish, but take care that it doesn't boil.
Remove the orange and the cinnamon sticks, then VERY CAREFULLY pour the mulled wine through a fine-mesh sieve into a large heat-proof bowl. Using the back of the spoon, press on the cranberries to get all of the juices into the bowl. A berry or two may burst, so watch out!
Return wine to the Crock Pot and stir in the brandy. Taste and add additional sugar until it's just sweet enough. I like it just past the pucker point; you may prefer a sweeter mulled wine.
Ladle into mugs and serve with a cinnamon stick, an orange slice, and/or fresh cranberries pushed onto a cocktail stick, if desired.
Keep your Crock Pot on the "warm" setting to keep the wine nice and hot. If your Crock Pot doesn't have a warm setting, try alternating between "low" and off.
A Crock Pot with a "warm" setting tends to work best for this recipe. Crock Pots do vary, but I've found if I keep it on low for more than three hours, it will boil - and you want to avoid boiling as it will burn off the alcohol.
Refined Sugar Free Option
Use pure maple syrup in place of the granulated sugar.