Here's the recipe I use for curried sweet potato soup - you could just substitute parsnips.
2 lbs sweet potatoes, peeled and cut into chunks
1 yellow onion, diced
some curry powder
4 cups of vegetable or chicken stock
1/4 cup of cream
Saute the onions in butter in a large pan about 10 - 15 minutes. Add the curry powder then the sweet potatoes. Stir together for a couple of minutes. Add stock. Cook for 45 minutes or until sweet potatoes are tender. Take off the heat. Blend until smooth. Stir in cream, s & p to taste. Garnish with dollop of yogurt. Add snipped chives if you're feeling sassy.