Melt butter in a skillet over medium heat. Add mushrooms and cook for 5 to 7 minutes, stirring occasionally, until browned and softened. Add shallot/onion, cook for 2 more minutes. Stir in garlic, thyme, soy sauce or Worcestershire, and a pinch of salt and pepper. Cook another 2 minutes until fragrant. Set aside and keep warm.

Mix ground beef with salt and pepper to taste and Worcestershire sauce. Divide the beef into 4 equal portions and gently shape into patties, slightly larger than your buns.

Heat a skillet or grill over medium-high heat. Add butter or oil and cook burgers for 3 to 4 minutes per side for medium, or to your preferred doneness.

During the last minute of cooking, place a slice of Swiss cheese on each patty and cover the pan (or close the grill lid) to melt.

While the burgers rest, lightly toast the buns cut-side down in the same skillet until golden.

Spread mustard or mayo on the buns if desired. Then, place the cheesy burger patties on the bottoms, top with the warm mushroom mixture, add any extra toppings you like, and close the sandwich.