Step 1: Prepare the Secret Sauce

In a small bowl, combine 1/4 cup of mayonnaise, 1 tablespoon of ketchup, 1 tablespoon of Dijon mustard, 1 teaspoon of pickle relish, 1/2 teaspoon garlic powder, 1/2 teaspoon onion powder, and 1/2 teaspoon of Worcestershire sauce. Stir well until smooth and creamy. Cover and refrigerate the sauce until you’re ready to use it.

Step 2: Caramelize the Onions

Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add the thinly sliced onions to the pan and season lightly with salt. Cook the onions for 15-20 minutes, stirring occasionally, until they become golden brown and caramelized. If the onions begin to stick or cook too fast, reduce the heat slightly and add a tablespoon of water to prevent burning. Once done, set the onions aside.

Step 3: Shape and Cook the Beef Patties

While the onions are caramelizing, divide the 1 lb of ground beef into four equal portions. Shape each portion into thin, square-shaped patties (to match the bread shape) and season both sides with salt and pepper. Heat a separate skillet or griddle over medium-high heat and cook the patties for about 3-4 minutes per side until they are browned and cooked through. Once cooked, set the patties aside.

Step 4: Assemble the Patty Melts

To assemble the patty melts, butter one side of each slice of rye or sourdough bread. Place one slice of Swiss cheese on the unbuttered side of four slices of bread. Top the cheese with one cooked beef patty, followed by some of the caramelized onions. Add another slice of Swiss cheese on top of the onions. Finish by spreading a generous spoonful of the secret sauce on the unbuttered side of the remaining bread slices, and place them sauce-side down to complete the sandwich.

Step 5: Grill the Patty Melts

Heat a clean skillet or griddle over medium heat. Place the sandwiches in the skillet and cook for 3-4 minutes per side, pressing down gently with a spatula, until the bread is golden and crispy, and the cheese has melted. Be careful not to burn the bread, and lower the heat if necessary.

Step 6: Serve

Once the sandwiches are golden and the cheese is oozing, remove them from the skillet. Slice each sandwich in half and serve hot. Don’t forget to drizzle a little extra secret sauce on top or serve it on the side for dipping!