Rinse the Cranberries: Start by rinsing the fresh cranberries under cold water, picking out any damaged or discolored ones.
Zest and Juice the Orange: Use a fine grater or zester to remove the zest from the orange. Then, cut the orange in half and juice it. You should have about 1/4 cup of orange juice.
Combine Ingredients: In a medium saucepan, combine the cranberries, sugar, water, orange zest, and orange juice. If you'd like to add cinnamon for extra flavor, you can do so now.
Cook: Place the saucepan over medium-high heat and bring the mixture to a boil. Reduce the heat to medium-low and let it simmer for about 10-15 minutes, or until the cranberries burst and the sauce thickens. You can use a spoon to gently press down on the cranberries to help them burst.
Stir Occasionally: Stir the sauce occasionally as it cooks to prevent sticking and ensure even cooking.
Taste and Adjust: Taste the cranberry sauce and adjust the sweetness to your liking. If it's too tart, you can add more sugar, a tablespoon at a time, until it reaches your desired sweetness. If it's too sweet, you can add a bit more orange juice or a splash of water.
Remove from Heat: Once the sauce has thickened and the cranberries have mostly burst, remove the saucepan from the heat.
Cool: Allow the cranberry sauce to cool in the saucepan for a few minutes.
Serve: Transfer the cranberry sauce to a serving dish and let it cool completely at room temperature. It will continue to thicken as it cools. You can serve it immediately, or cover it and refrigerate it until you're ready to serve.
Garnish (Optional): If you'd like, you can garnish your cranberry sauce with additional orange zest or a slice of orange for a festive touch.