01 -
Mix mayonnaise, ketchup, sweet pickle relish, and Worcestershire sauce in a bowl. Set aside
02 -
Cook sliced onions in butter over medium heat until golden brown, about 15-20 minutes
03 -
Form beef into 4 thin patties, season with salt and pepper, and cook 3-4 minutes per side
04 -
Butter rye bread slices. Layer Swiss cheese, patty, onions, and cheddar between bread slices
05 -
Cook assembled sandwiches until golden brown and cheese melts, about 2-3 minutes per side