1. Peel parsnips and carrots. Cut into 1/2-inch chunks.
2. In a 4- to 5-quart pan, combine parsnips, carrots, and 4 cups broth. Bring to a boil over high heat; reduce heat, cover, and simmer until vegetables are tender when pierced, 15 to 20 minutes.
3. Meanwhile, peel and core pears. Cut into 1-inch chunks. Add to pan and stir until hot, about 2 minutes.
4. With a slotted spoon, transfer carrots, parsnips, and pears, in batches if necessary, to a blender or food processor. Whirl until smooth, adding enough cooking liquid to purée easily. Return to pan with cooking liquid and stir until steaming. If necessary, add more broth to thin to desired consistency.
5. Ladle soup into bowls. Garnish with crème fraîche and chives. Add salt and pepper to taste.