In a bowl, combine your ground beef with a generous sprinkle of salt and pepper. Form into 4 patties, then set aside.

In a frying pan over medium heat, melt a tablespoon of butter. Toss in your sliced onions and sauté until they are soft and caramelized—about 8-10 minutes. Set those to the side for now.

In the same pan, add your beef patties and cook for about 4-5 minutes per side or until they reach your desired doneness. When they are almost done, place a slice of Swiss cheese on each patty and allow it to melt.

While the patties are cooking, let’s whip up the secret sauce! In a small bowl, mix together the mayonnaise, ketchup, Dijon mustard, pickle relish, garlic powder, salt, and pepper. Taste, and adjust seasoning if needed.

While your patties are finishing up, butter one side of each slice of rye bread. In a clean pan, place the slices butter-side down. Once golden brown, flip and assemble your melts.

On the unbuttered side of two pieces of bread, layer your delicious patty, a generous helping of caramelized onions, and a drizzle of that secret sauce. Top with another slice of bread, toasted side outward.

Grill each side until golden brown and heated through, about 3-4 minutes.

Cut those melts in half, plate, and serve!