Mushroom and Swiss Frisco burger | Recipe | Bounded by Buns

Ingredients

• 1 tablespoon olive oil
• 1 tablespoon butter
• 2 to 3 ounces sliced mushrooms
• 2 teaspoons all-purpose flour
• 1/4 cup beef or chicken broth
• 1 tablespoon marsala wine
• salt and ground black pepper
• 2 slices of sourdough bread
• 2 tablespoons butter, softened
• 1/3 pound ground beef (80/20)
• 2 slices of Swiss cheese
• 2 to 4 tablespoons mayonnaise
• 2 slices of cooked bacon (optional)
• mushrooms and sauce (from above)