1. In a large saucepan, bring cider to a boil and cook until reduced to 1 cup, about 40 minutes.
2. Combine reduced cider, cranberries, sugar, spices, salt and apple in a medium saucepan. Cook over low heat, stirring until sugar has dissolved. Simmer sauce until thickened and cranberries have popped, stirring occasionally, 10 to 12 minutes. (Sauce will thicken more when cool.)