Created by Devon on September 22, 2012
Step 1: Preheat grill or broiler to high heat. If using a broiler, line a baking sheet with aluminum foil.
Step 2: Grill the burgers turning once, until medium doneness, 7–8 minutes, or until well-done, 10–12 minutes (it will depend on the thickness of the burgers).
Step 3: Meanwhile, place the mushrooms, broth and soy sauce in a medium saucepan. Simmer for 2 minutes. Combine the cornstarch and 1/2 teaspoon cold water to form a paste. Stir the cornstarch mixture into the pot and cook until thickened, about 1 minute. Add salt and pepper.
Step 4: Place a slice of Swiss on each burger. Grill until the cheese is melted, about 1 minute longer.
Step 5: Split the hamburger buns and place a lettuce leaf on each bottom. Add a burger and spoon the mushroom sauce on top. Place the top of the buns on the burgers and serve immediately.