In a large skillet, melt 2 tablespoons of butter over medium heat. Add 8 ounces of sliced mushrooms and 1 small sliced onion, sautéing them for 8-10 minutes until they turn golden brown and fragrant. Incorporate 2 minced garlic cloves and 1 tablespoon of Worcestershire sauce, cooking for an additional minute. Finally, season the mixture with salt and pepper to taste, and set aside.

In a mixing bowl, gently combine 1 pound of ground beef with 1 tablespoon of steak seasoning and an additional dash of Worcestershire sauce. Avoid over-mixing to ensure tenderness. Form the mixture into 4 patties slightly larger than the burger buns, making a small indent in the center of each to prevent them from puffing up while cooking.

Preheat your grill or skillet to medium-high heat, aiming for around 375-400°F. Place the patties on the hot surface and cook for 3-5 minutes on each side, until they achieve a nice sear and are cooked through to your desired doneness. During the last minute of cooking, place a slice of Swiss cheese on each patty and cover to help it melt wonderfully.

While the patties are cooking, prepare the buns by brushing the cut sides of 4 brioche or potato hamburger buns with melted butter. Place them cut-side down in a separate skillet over medium heat and toast for 2-3 minutes until they become golden brown and slightly crispy, enhancing the overall texture of your Mushroom Swiss Burger.

Once everything is ready, it's time to assemble your Mushroom Swiss Burger! Start with the bottom half of each toasted bun and layer on a cheesy beef patty. Generously top the patty with the savory sautéed mushroom and onion mixture. Add any additional toppings you desire, like fresh greens or spicy condiments, before finishing with the top half of the bun.

Serve your delicious Mushroom Swiss Burger hot off the grill, ideally paired with crispy sweet potato fries or a vibrant garden salad for a complete meal. Gather your loved ones, and enjoy the burst of flavors in each messy, satisfying bite!