Rinse the cranberries under cold water and remove any stems or debris. Set them aside.
In a medium saucepan, combine the cranberries, sugar, orange juice, orange zest, water, and cinnamon stick (if using).
Over medium heat, bring the mixture to a gentle boil. Stir occasionally to prevent sticking.
Once it starts boiling, reduce the heat to a simmer. Continue cooking, stirring occasionally, for about 10-15 minutes. The cranberries will burst and the sauce will thicken.
If you prefer a smoother sauce, you can use the back of a spoon or a potato masher to crush the cranberries further. Remove the cinnamon stick if used.
Taste the sauce and adjust the sweetness by adding more sugar if desired. Remember, the sauce will thicken slightly as it cools.
Remove the sauce from the heat and allow it to cool to room temperature. Then transfer it to a serving bowl or airtight container. It will continue to thicken as it cools.
If you prefer your cranberry sauce chilled, cover and refrigerate for a few hours before serving.