Sweet potato pie is a traditional side dish or dessert in the Southern United States. It is often served during the American holiday season, especially at Thanksgiving, and is similar in many ways to pumpkin pie. Marshmallows are sometines added as a topping, but this was adapted more in the Northern United States than in the South. It is usually made as a large tart in an open pie shell without a top crust. The filling consists of mashed sweet potatoes, milk, sugar and eggs, flavored with spices such as cinnamon and nutmeg. Other possible ingredients include vanilla or lemon flavoring, maple syrup, molasses, and brown sugar. The baked custard filling may vary from a light and silky to dense, depending on the recipe's ratio of mashed potato, milk and eggs.