Apple Cider Donut Muffins with a Salted Caramel Filling are so easy to whip up and make the perfect fall treats. They're loaded with apple cider, cinnamon sugar and salted caramel in a poppable bite.: Apple Cider Donut Muffins with a Salted Caramel Filling are so easy to whip up and make the perfect fall treats. They're loaded with apple cider, cinnamon sugar and salted caramel in a poppable bite.