Root Vegetable Purée

This recipe was originally printed in Gourmet magazine, and is an easy side dish for Thanksgiving or any day.  Makes about 7 cups.

Ingredients:
3 lbs large boiling potatoes, peeled & quartered
1½ pounds turnips, peeled and cut into ½ inch chunks.
¾ pound carrots, sliced thin
¾ stick (6 Tablespoons) unsalted butter, cut into pieces and softened
⅓ Cup heavy cream, if desired

Procedure:

1. In large saucepan combine potatoes, with enough salted cold water to cover them by 1 inch, bring the water to a boil, and simmer potatoes for 10 to 15 minutes, or until they are tender.  While potatoes are cooking, in a steamer set over boiling water, steam the turnips and carrots, covered, for 15 minutes, or until they are very tender, and purée them in a food processor.
2. Drain the potatoes in a large colander, let them stand for 5 minutes and purée them.
3. Return to saucepan.  Add the butter, stirring until it is melted into the purée, add the turnip and carrot purée and season mixture with salt and pepper.  Add the cream if desired, and heat the purée over moderately low heat, stirring until it is hot.
4. The purée may be made 1 day in advance and kept covered and chilled.  Reheat the purée in the top of a double boiler set over simmering water, stirring, until it is hot.