Make your hamburger patties and slice the potatoes French fry style. Line your baking dish with aluminum foil, leaving enough extra to make a pouch. Take a stick of butter and rub on the aluminum foil to grease. Place your hamburgers on top of greased foil then add an onion slice and 1/2 pat of butter on top of each burger. Cover your burgers and any space space between them with the potatoes. Fold your aluminum foil into a pouch to seal. Bake at 350 degrees for 1 hour. About 50 minutes into baking, remove foil and top with cheese. Finish baking for the final 10 minutes.