Ingredients

• 1 1/2 pounds Yukon Gold potatoes
• 1 1/2 pounds celery root (celeriac)
• 1 cup heavy cream
• 1/4 cup chopped chervil

• Equipment: a food mill or potato ricer

 makes 4 servings
Preparation
Peel potatoes and celery root. Cut into 1-inch chunks. Steam in a large steamer set over boiling water, covered, until very tender, 30 to 40 minutes.
Force through food mill into a bowl. Stir in cream, chervil, 3/4 teaspoon salt, and 1/2 teaspoon pepper. Season with additional salt.
Cooks' note: Purée can be made 2 days ahead and chilled. Reheat gently.