Make the orange syrup: Peel one orange and squeeze out the juice (leave the other 1/2 orange for later). Place the zest on a cutting board, cut off the white pith (more or less) and discard it. Add the orange juice and zest, sugar and spices into a medium pot. Bring to a boil over medium heat and cook, stirring for about 3 minutes, then add the cranberries and cook for 2 more minutes. Sugar should dissolve, cranberries will slightly burst (when added earlier, they will break down completely), and the syrup will be thickened. Remove the pot from heat and let the syrup stand for 10 minutes until slightly cooled (this is optional).
Make the mulled wine: Add the wine, remaining ½ orange (cut into smaller pieces) and heat gently over minimum heat until the wine is very warm, but not boiling. If you bring the mulled wine to a boil, it will lose some of its aroma and alcohol will start to evaporate (and we don’t want that, right?). You can measure the temperature with a thermometer, it should be maximal 167°F / 75°C. If your mulled wine is not sweet enough, you can sweeten it with more sugar.
Serve: Take the pot off the heat, set aside for 5-10 minutes (optional). Strain the wine into a pitcher (you can discard the spices, oranges, and cranberries). Ladle the drink into heatproof glasses (thin wine glasses can break) and serve. For decoration, you can add spices from the pot, fresh cranberries, and orange pieces.
Cheers!