Peel parsnips; halve lengthwise and cut crosswise into 1/2-inch-thick slices. Peel sweet potatoes; cut into 1/2-inch cubes. Cut broccoli head from stem and separate into small florets, rinse well. In a large saucepan, bring water and salt to boiling. Add parsnips, sweet potato, and onion. Lower heat and simmer 6 minutes. Add broccoli flowerets; simmer 3 minutes or until all the vegetables are tender. Meanwhile, combine ricotta cheese, milk, potato flakes, pepper and nutmeg in a blender. Whirl until pureed. Stir ricotta mixture into soup until well blended. Gently heat through. Ladle into soup bowls and sprinkle with Parmesan cheese. Makes 4 servings.