Rinse cranberries and remove any soft or damaged berries. Set aside.

In a medium saucepan, combine sugar and water. Bring to a boil over medium-high heat, stirring until sugar dissolves completely.

Add cranberries to the boiling sugar water. Return to a boil, then reduce heat to medium.

Cook uncovered 10-12 minutes, stirring occasionally, until berries burst and sauce thickens.

Remove from heat and stir in orange zest if using. The sauce will continue to thicken as it cools.

Transfer to a serving bowl and let cool to room temperature. Refrigerate until ready to serve. Can be made up to 4 days ahead.