4 cups cranberries
2 Tablespoons fresh ginger, grated or minced
3 cups water
1 1/2 cups sugar
Boil everything together until tender, then let cool thoroughly in the fridge. Whiz in the (immersion) blender or run through a food mill (if you use a blender, there'll be little strings of cranberry peel, but they're not unpleasant).
Pour into container, cover, and place mixture in the freezer. When it is semi-solid, mash it up with a fork and refreeze again. When frozen, place in a food processor or (immersion) blender and process until smooth. Cover and refreeze until serving time.