Cost per Serving:
1. Mist a slow-cooker insert with cooking spray. Combine butter, onion, celery, carrot and garlic in slow cooker. Add eggplant, mushrooms and 1 tsp. salt. Stir in tomatoes, cover and cook on high for 4 hours or on low for 6 hours. Stir once or twice during cooking.
2. Bring a large pot of salted water to a boil and cook penne until just tender, about 10 minutes. Drain pasta, toss with sauce, sprinkle with basil (and grated Parmesan, if desired) and serve.