Heat a skillet over medium heat and add a little butter or oil.
Form the ground beef or turkey into patties and season with salt and pepper.
Cook the patties in the skillet until browned and cooked through, about 4-5 minutes per side.
Remove the patties and set aside. In the same skillet, add a bit more butter or oil if needed and sauté the sliced onions until caramelized.
Wipe the skillet clean and assemble the sandwiches. Place a slice of Swiss cheese on each slice of rye bread.
Place a patty on one slice of bread, top with caramelized onions, and cover with the other slice of bread with cheese.
Butter the outsides of the sandwiches.
Heat the skillet over medium heat and grill the sandwiches until golden brown and the cheese is melted, about 3-4 minutes per side.
Serve your Patty Melts hot and enjoy!