Make the Secret Sauce:

1. In a small bowl, mix mayonnaise, ketchup, sweet pickle relish, and Worcestershire sauce.
2. Stir well and set aside.

Caramelize the Onions:

3. In a large skillet, melt 1 tbsp butter over medium heat.
4. Add sliced onions and cook, stirring occasionally, until golden brown and caramelized (about 15-20 minutes).
5. Remove from skillet and set aside.

Cook the Beef Patties:

6. Divide ground beef into four thin patties, slightly larger than the bread slices (they will shrink when cooked).
7. Season both sides with salt and pepper.
8. In the same skillet, cook patties over medium-high heat for 3-4 minutes per side, until fully cooked.
9. Remove from skillet and set aside.

Assemble the Patty Melts:

10. Butter one side of each slice of rye bread.
11. Place four slices, butter-side down, on a clean skillet or griddle over medium heat.
12. On each slice, layer:

• 1 slice Swiss cheese
• 1 beef patty
• Caramelized onions
• 1 slice cheddar cheese
• Another slice of rye bread, butter-side up

Grill the Sandwiches:

13. Cook each sandwich for 2-3 minutes per side, until the bread is golden brown and crispy and the cheese is melted.

Serve:

14. Remove from skillet and let rest for 1 minute.
15. Slice in half and serve with the secret sauce on the side or drizzled on top.