Add all ingredients except rum to a small saucepan and stir together.
Cook over medium heat, until mixture starts to boil.
Reduce heat to medium low and continue cooking for another 20 minutes, occasionally stirring and squashing cranberries with a spoon
Stir in the rum and cook for another 5 min.
Remove cinnamon stick and discard. Squash berries further if you desire.Set sauce aside to cool The sauce can be made a couple days ahead and stored in the fridge until needed.Serve at room temperature