This diner favorite - ground beef, caramelized onions, and melted cheese between slices of grilled rye bread is easy to make at home. If you can find fresh Russian Rye, it's the best rye bread! It's usually found near the Deli and not in the bread aisle of the supermarket.
1-1/2 lbs. ground beef
Salt and freshly ground black pepper
5 Tbsp. Canola oil
1 large Vidalia onion (or 2 medium yellow), halved and thinly sliced
12 slices Russian Rye bread
12 thin slices cheddar, Swiss or American cheese
8 tbsp. unsalted butter, softened
Pickles for serving
Season the beef with salt and pepper. Divide the meat into six 1/4 inch patties that are slightly wider and longer than the bread slices.
Heat 2 Tbsp. oil in a 12-inch cast-iron skillet over medium-high heat. Add the onions, season with salt and pepper and cook, stirring until softened and browned, about 10 minutes.
Transfer the onions to a bowl; wipe out the skillet. Working in 3 batches, heat 1 Tbsp. oil in same skillet over high heat. Add 2 burger patties and cook, flipping once, until well browned, about 4 minutes.
Top each of 6 bread slices with some of the onions, a cheese slice and burger patty. Top each burger with another cheese slice and bread slice. Spread butter over the top and bottom of each sandwich.
Cook the sandwiches, flipping once, until golden brown and warmed throughout.