Prepare the mixture for meatballs of minced meat, egg, finely grated potatoes, grated 2/3 of the cheese, chopped parsley, salt and pepper. Spread rectangular tray with margarine and partition the mixture formed into a roll. Well washed and cleaned mushrooms are arranged on both sides of the roll, sprinkle with pepper and salt and broken lumps butter, and top Grate the remaining cheese. Bake in preheated oven to 200 C to redness of the roll.