1. Combine orange juice, sugar and cinnamon stick in a heavy 2-quart saucepan. Bring to a simmer over medium heat, stirring until the sugar dissolves.
2. Stir in cranberries and orange zest. Turn heat down and, stirring often, simmer until the berries burst and the sauce thickens slightly, about 15 to 20 minutes.
3. Transfer sauce to a heatproof glass container and cool for 30 minutes. Cover and refrigerate until serving time.
4. Just before serving, remove cinnamon stick and stir in whisky, if desired.