Two tablespoons of the butter will need to be softened or melted in order to be incorporated into the purée. If you choose to use the celeriac cooking liquid in place of the white wine, you may want to stir in a splash of lemon juice at the end.

3 c peeled, chopped celeriac (roughly 2-inch pieces)
2 c peeled, cored, chopped pears (roughly 1-inch pieces)
4 T unsalted butter, divided
1/2 c dry white wine or celeriac cooking liquid
1/4 c heavy cream
pinch nutmeg or cinnamon or cardamom
salt and pepper, to taste
a splash of lemon juice, optional

1. Place the chopped celeriac in a saucepan, and cover with water. Bring to a boil. Lower the heat and simmer, covered (or not), until tender, about 20 minutes (the time will depend on the size of the pieces). Drain in a colander, reserving cooking liquid, if you like.

2. Meanwhile, in a large skillet, melt 2 tablespoons of the butter over medium heat. Add the pears and cook, stirring, until soft, about 5 minutes. Add the wine or celeriac cooking liquid and cook, stirring, until thick and the pears fall apart. Remove from the heat.

3. Transfer the drained celeriac and pears to a food processor. Add the cream and remaining 2 tablespoons of butter and purée until smooth. Season with the nutmeg, salt, and pepper. Taste, and add some lemon juice if you think it needs it.