Mix the ingredients. Combine the cranberries, sugar, orange juice, zest, cinnamon stick, grand marnier, and water in a small saucepan and stir well.
Simmer. Bring to a gentle simmer over medium-low heat for 15-20 minutes, stirring occasionally. Discard the rosemary. Even if the sauce looks thin, it'll thicken up in the fridge. If you like a very thick cranberry sauce, simmer a little longer.
Cool and refrigerate. Let the cranberry sauce cool to room temperature, then transfer to an airtight container in the fridge for 2 hours before serving. The cranberry sauce can be made several days in advance and stored in the fridge.