In a small bowl, whisk together the mayonnaise, ketchup, Dijon mustard, garlic powder, salt, and pepper. Adjust the seasoning according to your taste.

In a skillet over medium heat, melt a tablespoon of butter. Add the sliced onions, season with a pinch of salt, and sauté until they’re soft and slightly caramelized, about 5-7 minutes.

Shape the ground beef into four patties and season both sides with salt and pepper.

In the same skillet, increase the heat to medium-high, add a little more butter, and cook the patties for about 4-5 minutes on each side or until they reach your desired doneness. Top each patty with a slice of Swiss cheese in the last minute of cooking.

Spread a generous dollop of the secret sauce on one slice of rye bread. Top it with a cheesy patty, some sautéed onions, and another slice of bread.

In the same skillet, add a little more butter. Grill each sandwich until golden brown and crispy, approximately 2-3 minutes per side.

Slice your Patty Melts in half and serve them warm with extra secret sauce on the side.