Start by rinsing 12 ounces of fresh cranberries under cold water; inspect them for any bad ones and discard. In a medium saucepan, combine the cleaned cranberries with 1 cup of water and bring to a gentle boil over medium heat. Watch as the cranberries begin to pop.

Once the cranberries have burst, lower the heat and stir in 1 cup of brown sugar. Keep stirring for about 2-3 minutes until the sugar completely dissolves, creating a vibrant sauce.

Add 1/4 cup of dark rum and a cinnamon stick to the saucepan, continuing to simmer for another 10 minutes.

Remove the saucepan from heat and stir in 4 tablespoons of unsalted butter, allowing it to melt completely into the sauce.

Transfer the sauce to a heat-proof bowl and let it cool for about 30 minutes. Once slightly cooled, cover and refrigerate it for at least 2 hours.

Garnish the sauce with a sprinkle of chopped nuts or a zest of orange before serving.