Fry the onions over low heat. Then put the mushrooms and finally chicken. This mixture is placed in the center of the tray in the shape of a circle. Make mashed potatoes. Put it in the tray to cover the remainder, about fried chicken. Baked for about 15 minutes. Remove and pour the beaten egg and milk, which are mixed together. Bake to redness. Remove from the oven and sprinkle with grated cheese and leave again in the oven until browned cheese.