Unsalted butter: Also called "sweet butter," this is just butter that has been produced without adding salt. It is served in many restaurants and is most available and most popular on the East and West coasts in America. It accounts for a very small proportion of the butter sold. Upside-down cake: A traditional cake in which butter, brown sugar and sometimes spices are heated in a cast-iron skillet or a baking pan until blended. Fruit, most often pineapple, is added and topped with cake batter to make 1 layer. After baking, the cake is inverted to reveal the fruit and brown sugar topping.