Christopher Kimball visits Cheryl Day at Back in the Day Bakery in Savannah, Georgia, to learn treasured recipes from her repertoire of southern baking. Sweet Potato Cupcakes with Cream Cheese-Caramel Frosting; Glazed Sour Cream and Brown Sugar Bundt Cake, inspired by old-fashioned butterscotch candies; and a grand, show-stopping Chocolate-on-Chocolate Three-Layer Cake.