This is from "The Produce Bible," by Leanne Kitchen. I like that it uses vegetables that are in season in the winter, and it's a nice alternative for mashed potatoes.
1 leek, white part only, thinly sliced
3 large parsnips, peeled and chopped
2 Tbs snipped chives
2 Tbs butter
3 Tbs creme fraiche
Put the leeks and parsnips in a saucepan of boiling salted water. Cook for about 10 minutes, until tender. Drain and allow to cool slightly before blending in a food processor to a smooth puree.
Put the puree in a clean saucepan and add the chives and butter. Season with sea salt and fresh ground pepper. Cook the puree until heated through. Remove from the heat and stir in the creme fraiche.