Start by heating the butter and olive oil in a large skillet over medium heat. Once the butter melts, add the sliced mushrooms. Sauté them for about 5 minutes until they’re golden brown. Stir frequently to ensure even cooking. Add the minced garlic and cook for another minute.

Next, pour in the Worcestershire sauce and beef broth, followed by the black pepper, balsamic vinegar, and thyme. Mix well and simmer for about 10 minutes, allowing the flavors to meld. The mushrooms should be juicy and flavorful but not swimming in liquid.

In a mixing bowl, combine the ground beef, Worcestershire sauce, and steak seasoning. Do not overmix! Gently shape the mixture into four equal-sized patties. Make a small indentation in the center of each patty; this helps prevent them from puffing up while cooking.

Preheat your grill or skillet over medium-high heat. Once hot, add the patties. Cook for about 4-5 minutes on each side for medium-rare, or adjust the time based on your preferred doneness. During the last minute of cooking, place a slice of Swiss cheese on top of each patty and close the lid to melt the cheese.

While the patties finish cooking, you can toast your brioche buns. Lightly butter the insides and place them face down on the grill for a minute or two until golden. This adds a delightful crunch to the burger’s structure.

Now comes the fun part! Place the burger patty with melted Swiss cheese on the bottom bun. Generously top it with the sautéed mushrooms. Finish with the top bun and press down slightly. If desired, you might want to add condiments like mayonnaise or mustard for an extra layer of flavor.