Wash clementines thoroughly. Using a fine grater or zester, zest all three clementines, being careful to only get the orange part and avoid the bitter white pith. Set zest aside. Halve the zested clementines and juice them, collecting the juice in a separate bowl. You should have about 1/2 cup of juice.

In a medium saucepan, combine the fresh cranberries, granulated sugar, water (or orange juice), clementine juice, and pinch of salt. If using, add the ground cinnamon.

Place the saucepan over medium heat. Bring the mixture to a gentle boil, stirring occasionally until the sugar dissolves.

Once boiling, reduce the heat to medium-low and simmer for 10-12 minutes, stirring occasionally. The cranberries will begin to burst and soften, thickening the sauce. Use the back of your spoon to gently mash some of the cranberries against the side of the pan if you prefer a smoother sauce.

Remove the saucepan from the heat. Stir in the reserved clementine zest. This is added at the end to preserve its bright, fresh flavor.

Transfer the Cranberry Clementine Sauce to a bowl or jar. Allow it to cool completely at room temperature. The sauce will thicken further as it cools. Serve chilled or at room temperature.