A cheeseburger is a hamburger topped with cheese. Traditionally, the slice of cheese is placed on top of the meat patty, but the burger can include many variations in structure, ingredients, and composition. The cheese is normally added to the cookinghamburger patty shortly before serving, which allows the cheese to melt. As with other hamburgers, a cheeseburger may include toppings, such as lettuce, tomato, onion, pickles, mustard, mayonnaise, ketchup, or bacon; examples of less common toppings might be spinach or olives.
In fast food restaurants, the cheese used is normally processed cheese, but essentially any other meltable cheeses may be used—common examples include cheddar, Swiss, mozzarella, blue cheese, and pepper jack. Very soft/wet cheeses that melt poorly— like creamcheese, cottagecheese, or ricotta —are very unusual, and very hard /dry cheeses like Parmigiano-Reggiano (or its imitation, "parmesan") would rarely be used in quantities sufficient to be a recognizable topping as opposed to a seasoning.
