Preparation: Form the ground beef into 2 or 4 equal-sized patties (depending on desired serving size) and season them generously with salt, pepper, and optional garlic powder or Worcestershire sauce.

Caramelize the Onions: In a skillet, heat olive oil over medium-low heat. Add the sliced onions and cook, stirring occasionally, for 20-25 minutes until they are golden brown and caramelized. Set aside.

Cook the Patties: In the same skillet, increase the heat to medium-high. Add the beef patties and cook for about 3-4 minutes on each side, or until they are browned and cooked to your desired doneness. Set aside on a plate.

Assemble the Patty Melt: Butter one side of each slice of rye bread. On the non-buttered side of two slices, place one slice of Swiss cheese, followed by a cooked beef patty, a generous portion of caramelized onions, and another slice of Swiss cheese. Top with the other buttered slices, buttered side up.

Grill the Sandwiches: In a skillet or griddle, cook the assembled sandwiches over medium heat for about 3-4 minutes on each side, or until the bread is golden brown and crispy, and the cheese is melted.