Begin by zesting one large orange to get about 1 teaspoon of zest. Then, juice the orange to measure out 1/4 cup of fresh orange juice.

Rinse the cranberries under cold water, and set aside 1/2 cup of the berries for later use.

In a medium saucepan, combine the remaining cranberries, water, orange juice, and brown sugar. Place over medium heat and stir occasionally until the mixture reaches a simmer.

Once simmering, reduce the heat to low-medium. Continue cooking for about 15 minutes, stirring occasionally, until the cranberries have burst and the sauce has thickened.

Remove the saucepan from the heat and stir in the reserved 1/2 cup of cranberries, the orange zest, and vanilla extract (optional).

Allow the sauce to cool, during which it will thicken further. Serve the cranberry sauce warm or at room temperature.