Grilled Cheese
Evidence indicates that, in the U.S., the modern version of the grilled cheese sandwich originated in the 1920s when inexpensive sliced bread and American cheese became readily available. According to foodtimeline.org, John Montagu, fourth Earl of Sandwich invented the sandwich.
In addition to the North American Grilled Cheese, there are the French Croques, Swiss' Croûtes, Welsh Rarebits, British Toasties and Italian Paninis, just to name a few. It is safe to say that melted cheese is loved the world round.