What cheese is traditional on a patty melt?

Swiss cheese is the traditional cheese on a patty melt.

A classic patty melt combines a ground-beef patty, melted Swiss cheese, and usually caramelized onions between two slices of griddled bread. The bread is commonly caraway-seeded rye or marbled rye rather than a standard hamburger bun, giving the sandwich its recognizable diner-style character.

The patty melt is often described as a hybrid of a cheeseburger and a grilled cheese sandwich. The bread, beef, cheese, and onions are cooked or assembled so the exterior becomes crisp while the cheese melts around the patty. It is usually served without the elaborate toppings associated with many modern burgers.

Its exact origin is uncertain, but the sandwich became associated with mid-20th-century American diners. Los Angeles restaurateur Tiny Naylor is frequently credited with helping popularize it; the sandwich appeared at Tiny Naylor’s restaurants in the early 1950s, although claims that he invented it are not settled.

Swiss cheese is traditional, not mandatory. Restaurants and home cooks sometimes substitute American cheese, cheddar, provolone, or other varieties. That flexibility does not change the standard answer to a question asking which cheese is traditional: Swiss cheese remains the canonical choice.