A mixture of eggs, seasonings and sometimes water or milk, cooked in butter until firm and filled or topped with various fillings such as cheese, ham, mushrooms, onions, peppers, sausage and herbs. Sweet omelets can be filled with jelly, custard or fruit, sprinkled with confectioners' sugar or flamed with various liquors or liqueurs. For fluffy omelets, the whites and yolks can be beaten separately and folded together. They can also be served flat or folded. See also frittata.