Bring a large pot of salted water to a boil. Boil cabbage 12 to 15 minutes, removing 9 leaves as they become pliable. Drain well, then remove tough stem from leaves; cut leaves in half. Remove remaining cabbage from water and shred. Place shredded cabbage in bottom of slow cooker.
Meanwhile, heat oil in a large nonstick skillet over medium heat; cook onion 5 minutes. Add garlic, cinnamon and nutmeg; cook 1 minute. Remove half of onion mixture; set aside. Stir tomato sauce, sugar and vinegar into skillet and remove from heat.
Pulse bread and milk in food processor until a paste is formed. Add reserved onion mixture, beef, salt and pepper to food processor and pulse until well combined.
With stem ends of cabbage leaves facing you, place 2 heaping tbsp of meat mixture in center of each leaf and roll up. Place rolls, seam-side down, in slow cooker. Pour sauce over top. Cover; cook on LOW for 5 hours. Serve with noodles.