Ultimate Patty Melt with Secret Sauce

1 lb ground beef
8 slices of rye bread
8 slices of Swiss cheese
1 large onion, thinly sliced
4 tbsp butter, plus more for spreading
Salt and pepper to taste
For the Secret Sauce:
1/2 cup mayonnaise
2 tbsp ketchup
1 tbsp relish
1 tsp Worcestershire sauce
1/2 tsp garlic powder
1/2 tsp onion powder
Salt and pepper to tasteBegin by mixing the secret sauce ingredients in a small bowl. Adjust seasoning to taste, then set aside.
In a skillet over medium heat, melt 1 tbsp of butter. Add the thinly sliced onions, season with salt and pepper, and cook until caramelized, about 10-15 minutes. Transfer to a plate.
Form the ground beef into 4 patties, slightly larger than your bread slices. Season both sides with salt and pepper.
In the same skillet, cook the patties to your desired doneness, about 4 minutes per side for medium. Remove and set aside.
Butter one side of each bread slice. To assemble, spread the secret sauce on the non-buttered side of 4 slices, add a slice of cheese, a patty, caramelized onions, another slice of cheese, and top with another bread slice, buttered side up.
In a clean skillet over medium heat, grill the sandwiches until golden brown and the cheese is melted, about 3-4 minutes per side.
Prep Time: 15 minutes | Cooking Time: 30 minutes | Total Time: 45 minutes
Kcal: 650 kcal | Servings: 4 servings