The patty melt I know is, ideally:
Rye bread, grilled
Cheese, melted: can be swiss or cheddar
ground beef patty
I maintain that the defining characteristics of a patty melt are the patty and the melted cheese on grilled bread. Meaning the onions can be committed and the types of bread and cheeses can change.
A friend insists that it isn’t a patty melt without onions, and it’s dicey if the bread isn’t rye.
The Dope says?