Rinse the cranberries under cool water and remove any stems or bad berries. Zest the orange before juicing it.
In a medium saucepan, combine the cranberries, sugar, orange juice, orange zest, and cinnamon (if using).
Cook over medium heat, stirring occasionally. As the mixture heats, the cranberries will begin to pop—this is normal!
Once the mixture reaches a gentle boil, reduce the heat to low and let it simmer for about 10 minutes. Stir occasionally.
The sauce will thicken as it cools. If you like a chunkier texture, mash some of the cranberries with the back of a spoon.
Remove the saucepan from heat and let the sauce cool to room temperature. Transfer to a serving dish or store in an airtight container in the refrigerator.
