The burger sandwich made by griddling a beef patty with melted cheese between two slices of bread is a patty melt.
A patty melt usually contains a thin ground-beef patty, melted cheese, and grilled onions. Instead of a hamburger bun, it uses sliced bread, commonly rye bread. The assembled sandwich is cooked on a griddle or skillet until the bread is browned and crisp and the cheese has melted.
The patty melt became especially popular in American diners and luncheonettes during the mid-twentieth century. Its exact inventor is uncertain, although Los Angeles restaurateur Tiny Naylor is frequently associated with popularizing the sandwich in the 1940s.
A patty melt is often mistaken for a grilled cheeseburger because both are griddled and include cheese. The bread is the clearest distinction: a traditional patty melt uses slices of bread, while a conventional hamburger uses a split bun. Rye bread and grilled onions are also characteristic, though recipes can vary.