Too tart to eat raw and on their own, cranberries are delicious in sweet relishes, sauces, breads and other preparations. Most of the autumn harvest ends up in canned cranberry sauce and bottled juice. Because cranberries marry well with other fruits, their juice often is sold mixed with apple, raspberry or another fruit juice. It also is bottled with white grape juice to sweeten it. This sorbet calls for unsweetened juice, which can be found in natural-foods stores. The recipe adds just the right amount of sugar for a refreshing, elegant dessert.