Best Swiss Mushroom Burger Recipe is a show-stopping gourmet burger filled with delicious caramelized onions and mushrooms, and Swiss cheese! Ingredients: 1½ pound steak piece cut into thin slices 1 tablespoons salt and pepper 4 slices of Swiss cheese or shredded Swiss cheese 4 brioche buns 3 tablespoons unsalted butter 1 pound white mushrooms sliced […]