01 -
In a small bowl, mix together the mayo, ketchup, pickle relish, and Worcestershire until smooth. Put it aside.
02 -
Heat 1 tbsp of butter on medium in a big pan. Stir the sliced onions now and then, letting them caramelize for 15-20 minutes. Take them out when ready.
03 -
Shape the beef into 4 thin patties. Sprinkle some salt and pepper on top. In the same pan, cook them on medium-high for 3 to 4 minutes on each side. Set them aside when done.
04 -
Spread butter on one side of every bread piece. Build your sandwich with the buttered side out: bread first, then Swiss cheese, a patty, onions, cheddar, and finish with more bread (buttered side up). Toast each side for 2-3 minutes until golden brown and melty.
05 -
Give the sandwiches a minute to rest. Cut into triangles and either dip in the sauce or pour it on top to enjoy!