Preheat oven to 350 degrees. Chop onion. Saute the onion in small amount of butter until clear. Set aside. Soak the bread in milk. Mix the sautéed onion, bread which has been soaked, and chop meat in a bowl. Add egg and mix thoroughly. Form into loaf and place in meatloaf pan. (A pan with insert which allows any fat drippings to go through holes in the bottom.) Brush top with either ketchup or tomato sauce. Bake at 350 degrees for 30-45 minutes or to your desired browning. When removed from oven, allow to sit for 5 minutes, then slice and serve.