Step 1: Make the Secret Sauce

1. In a small bowl, whisk together mayonnaise, ketchup, pickle relish, Dijon mustard, garlic powder, and smoked paprika until smooth.
2. Set aside in the refrigerator while you prepare the patty melts.

Step 2: Caramelize the Onions

1. Heat 1 tablespoon of butter in a large skillet over medium heat.
2. Add the sliced onions, a pinch of salt, and cook, stirring occasionally, until golden and caramelized (about 10-12 minutes). Remove from the skillet and set aside.

Step 3: Cook the Beef Patties

1. In a mixing bowl, combine ground beef, Worcestershire sauce, garlic powder, salt, and pepper. Divide into 4 equal portions and shape into thin patties roughly the size of your bread slices.
2. Cook the patties in the same skillet over medium-high heat for 3-4 minutes per side, or until browned and cooked to your desired doneness. Set aside.

Step 4: Assemble the Patty Melts

1. Spread a thin layer of butter on one side of each bread slice.
2. Place a slice of cheddar cheese on the unbuttered side of 4 bread slices. Top with a beef patty, caramelized onions, Swiss cheese, and a drizzle of the secret sauce. Place another slice of bread on top, buttered side out.

Step 5: Grill the Sandwiches

1. Heat a clean skillet or griddle over medium heat.
2. Cook each sandwich for 2-3 minutes per side, pressing gently with a spatula, until the bread is golden brown and the cheese is melted.

Step 6: Serve and Enjoy

1. Slice the sandwiches in half and serve warm with extra secret sauce on the side for dipping.