Serious Eats - seriouseats.com

To me, a hamburger needs to have two qualities to be justified as one: being made from hamburger, and having something to turn into a sandwich. If that's a bun, or toast, or lettuce doesn't matter to me.

You can't really split hairs on the patty melt if you accept toast but not sourdough. It's an accepted bread item holding a hamburger.

Jack In The Box had a patty melt a few years ago, but I never had the courage to try it as I actually do love patty melts, and I think I'll stay away from Carl's Jr.'s attempt as well.

You can't be serious. A burger is a burger regardless of your means of conveyance. Frankly, I think that buns are overrated. They are nice and all, but I actually prefer using a couple of pieces of toast instead of a bun; it's less bread to get in the way of the meat. Don't get this statement misconstrued, I won't turn down a bun, but I'll choose a couple slices of toast if I have the option.