Explain to someone who has never had a patty melt, what is it? It looks like a cheeseburger on 2 pieces of toast? Is that the difference between it and a cheeseburger?
It's made with rye bread, hamburger patty, grilled onions, and cheese (usually Swiss).
Cook the hamburger patty and the onions, and assemble.
Butter outside of bread, place on griddle or in a frying pan to crisp up the bread, flip and do other side.
One of my favorite sandwiches.