Drop cabbage leaves in salted water and boil for 3 minutes. Drain well. Trim off thick stem. Filling: Combine beef, rice, onion, egg, salt and pepper, and milk. Mix well and divide into 12 portions. Place one portion into the centre of each leaf and roll tightly burrito style. Fasten with a toothpick and place in baking dish. Sauce: combine tomato sauce, diced tomatoes, sugar, vinegar and water and cornstarch mixture and poor over rolls. Bake at 350 for one hour. Serve with sauce.