Place the celery root in a saucepan, and cover with water. Bring to a boil. Lower the heat and simmer, covered, until tender, about 20 minutes. Drain in a colander.
Meanwhile, in a large skillet, melt 2 tablespoons of the butter over medium-high heat. Add the pears and cook, stirring, until soft, about 5 minutes. Add the wine and cook, stirring, until thick and the pears fall apart. Remove from the heat.
Return the drained celery root and pears to a food processor. Add the cream and remaining 2 tablespoons of butter and puree until smooth. Season with the nutmeg, and salt and pepper to taste.