1 1/2 pounds hamburger
1/4 cup finely diced onion
1/2 teaspoon salt
1/8 teaspoon pepper
2 tablespoons butter or margarine
1/2 pound sliced mushrooms
6 slices cheddar cheese

Combine the hamburger, onion, salt and pepper. Mix well. Saute mushrooms in butter until slightly browned and softened. Form meat mixture into 12 patties, about a quarter inch thick. Spoon about 1/6 of the mushrooms on to half the patties. Top with cheese and second patty. Seal around the edges, making sure that the patties are good and solid. Place on preheated grill and cook for a couple minutes per side. Remove when done and serve.