01 -
Heat butter in a skillet over medium heat. Add mushrooms and onions, cook without stirring for 2 minutes to sear, then stir. Continue cooking, stirring occasionally, for 8 to 10 minutes until caramelized. Add minced garlic during the last minute of cooking. Stir in Worcestershire sauce, salt, and pepper, then remove from heat.
02 -
Gently combine ground beef with steak seasoning and Worcestershire sauce. Divide mixture into four equal portions and shape into patties slightly larger than buns. Make a shallow indentation in the center of each patty to prevent doming during cooking.
03 -
Heat a grill or skillet to medium-high. Sear patties for 3 to 5 minutes per side, avoiding pressing to retain juices. In the last minute of cooking, place Swiss cheese slices on each patty and cover to melt.
04 -
Brush cut sides of brioche buns with butter. Toast in a skillet or under a broiler until golden brown, approximately 30 to 60 seconds.
05 -
Place the cheese-topped patty on the bottom half of each toasted bun. Spoon a generous amount of the mushroom topping over the patty. Add condiments as desired, then close with the top bun.