In a mixing bowl, combine ½ cup mayonnaise, 1 tablespoon Dijon mustard, 2 tablespoons dill pickle relish, and 2 tablespoons ketchup. Stir until smooth and refrigerate for at least 10 minutes.

Slice one medium onion and sauté in 2 tablespoons of butter over medium-low heat. Add 1 tablespoon Worcestershire sauce and 1 tablespoon red wine vinegar, cooking for about 20 minutes until caramelized.

Shape ½ pound ground beef into two patties, season with salt, pepper, 1 tablespoon Worcestershire sauce, and a dash of mustard. Cook in a skillet over medium-high heat for 4 minutes on each side.

Butter one side of two slices of rye bread. Layer with muenster cheese, cheddar cheese, a patty, and caramelized onions. Top with another slice of bread, buttered side up.

Grill the patty melt in a skillet over medium heat for 3-4 minutes on one side. Press down gently with a spatula. Flip and grill another 3-4 minutes until golden and crispy.

Remove from skillet, allow to cool slightly, slice in half, and serve hot with crispy French fries or salad.