1. Prepare the Secret Sauce: The Key to Flavor

1. Combine Ingredients: In a small bowl, combine the mayonnaise, ketchup, sweet pickle relish, and Worcestershire sauce.
2. Mix Well: Whisk the ingredients together until they are thoroughly combined and the sauce is smooth.
3. Set Aside: Cover the bowl and set the secret sauce aside at room temperature while you prepare the other components. This allows the flavors to meld.

2. Caramelize the Onions: Sweet and Savory Depth

1. Melt Butter: In a large skillet (cast iron preferred), melt 1 tablespoon of butter over medium heat.
2. Add Onions: Add the thinly sliced onions to the skillet.
3. Cook Slowly: Cook the onions, stirring occasionally, until they are deeply caramelized and softened, about 15-20 minutes. This slow cooking process brings out the natural sweetness of the onions.
   • Tip: Don’t rush the caramelization process. Low and slow is the key to achieving that perfect sweet and savory flavor.
4. Remove from Skillet: Once caramelized, remove the onions from the skillet and set them aside.

3. Cook the Beef Patties: Juicy and Flavorful

1. Shape Patties: Divide the ground beef into 4 equal portions (about 4 ounces each). Gently shape each portion into a thin, oval patty that’s slightly larger than the slices of rye bread.
   • Tip: Don’t overwork the meat, as this can make the patties tough.
2. Season Patties: Season both sides of the patties generously with salt and pepper.
3. Cook Patties: In the same skillet you used for the onions, cook the patties over medium-high heat until they are cooked through, about 3-4 minutes per side for medium doneness.
   • Tip: For a juicier patty, avoid pressing down on them with a spatula while they’re cooking.
4. Remove from Skillet: Once cooked, remove the patties from the skillet and set them aside.

4. Assemble the Patty Melts: Building Layers of Flavor

1. Butter Bread: Butter one side of each slice of rye bread.
2. Place Bread in Skillet: Place 4 slices of rye bread, butter-side down, in a clean skillet or on a griddle over medium heat.
3. Layer Ingredients: Top each slice of bread with a slice of Swiss cheese, a cooked patty, a generous portion of caramelized onions, and a slice of cheddar cheese.
4. Top with Bread: Top with the remaining 4 slices of rye bread, butter-side up.

5. Grill to Golden Perfection: Melting the Cheese and Toasting the Bread

1. Cook: Cook the patty melts until the bread is golden brown and crispy, and the cheese is melted and gooey, about 2-3 minutes per side.
   • Tip: Use a spatula to gently press down on the patty melts while they’re cooking to help the cheese melt evenly.
2. Flip Carefully: Carefully flip the patty melts using a spatula.

6. Serve and Enjoy: The Ultimate Comfort Food Experience

1. Rest: Once done, remove the patty melts from the skillet and let them rest for a minute or two before slicing. This allows the cheese to set slightly.
2. Slice: Slice each patty melt in half diagonally.
3. Serve Immediately: Serve immediately with the secret sauce on the side for dipping, or drizzled over the top.