01 -
Heat butter and oil in a large pan over medium heat. Add sliced onions and sauté until softened and golden, about 6-8 minutes. Stir in mushrooms, season with salt, pepper, and optional Worcestershire sauce. Continue cooking until mushrooms are tender and most liquid has evaporated. Remove from heat and set aside.
02 -
Season ground beef with salt, pepper, and garlic powder. Shape into four oval, flat patties sized to fit the bread. Cook patties in a skillet over medium-high heat, browning each side until fully cooked through. Remove from skillet and set aside.
03 -
Butter one side of each slice of bread evenly. Place half the bread slices, buttered side down, in a skillet over medium heat. Layer with Swiss cheese, a cooked beef patty, sautéed mushrooms and onions, another slice of Swiss cheese, then top with a second buttered bread slice (buttered side up).
04 -
Cook assembled sandwiches over medium heat until bread is crisp and golden, about 3–4 minutes. Gently flip and cook the other side until browned and cheese is thoroughly melted.
05 -
Remove from skillet, slice in half, and serve promptly while hot.