Cranberries
Small, red, very tart berries, sold fresh, frozen, or dried and sweetened.
Fresh cranberries are mostly found in supermarkets from October to January, frozen ones sometimes year-round. Dried, sweetened cranberries are available everywhere but are much sweeter and cannot stand in for fresh berries.
Substitute:
Lingonberries, fresh or as a compote, come closest in tartness and colour, but they are smaller and softer and break down sooner; compote is already sweetened, so use less sugar.