01 -
Mix mayonnaise, Dijon mustard, barbecue sauce, and hot sauce in a small bowl until smooth.
02 -
Combine ground beef, Worcestershire sauce, salt, and black pepper in a large mixing bowl. Mix gently until just incorporated.
03 -
Divide beef mixture evenly and form into 6 oval-shaped patties of uniform thickness.
04 -
Melt butter in a skillet over medium heat. Add sliced onions and cook, stirring occasionally, until soft and golden brown.
05 -
Heat a skillet over medium-high heat. Cook patties for 2 minutes per side until browned but juicy. Remove patties and wipe skillet clean.
06 -
Spread a thin layer of butter on the outer sides of each bread slice. Place buttered side down on skillet. Layer with sauce, caramelized onions, a slice of cheese, one beef patty, another slice of cheese, more onions and sauce, and top with another bread slice, buttered side up.