Cook the mushrooms

• Melt the butter on the griddle over medium heat.
• Add the sliced mushrooms and cook until golden and tender.
• Season with salt and black pepper, then set aside.

Toast the buns

• Place the split buns cut-side down on the griddle.
• Toast until golden, then set aside.

Smash the patties

• Place the beef balls on the hot griddle.
• Smash each one flat with the spatula.
• Season with salt and black pepper.

Sear and flip

• Cook until the edges are browned and crisp.
• Flip the patties and cook the second side.

Melt the cheese

• Top each patty with Swiss cheese slices.
• Let the cheese melt over the patties.

Assemble the burgers

• Place the patties on the toasted bun bottoms.
• Spoon the cooked mushrooms over the cheese.
• Close with the bun tops and serve.