1. Place mushrooms in a medium bowl. Cover with warm water and let stand for 15 minutes. Lift mushrooms out of water, leaving liquid and sediment in bowl. Pat mushrooms dry with paper towels and chop finely. Discard soaking liquid.
2. In a food processor, pulse onion, garlic, carrot, leek and celery until coarsely chopped. In a large pot, warm oil over medium heat. Stir in onion mixture and mushrooms, sprinkle with salt and cook, stirring frequently, until vegetables are soft but not browned, 8 to 10 minutes. Add lentils, herbs, bay leaf, wine, if desired, and milk and cook, stirring occasionally, until liquid has nearly evaporated, 2 to 3 minutes. Stir in tomatoes and tomato paste, scraping bottom of pot. Reduce heat to low, cover and cook for 10 minutes longer, stirring to prevent scorching (sauce will be very thick). Season with salt and pepper.
3. Remove bay leaf and spoon sauce on top of pasta. Sprinkle with grated Parmesan, if desired, and serve.