How to Make It
In a large saucepan, combine the celery roots with the cream and water and bring to a boil. Cover and simmer over moderately low heat until tender, about 30 minutes. Uncover and cook over high heat until the cream is thickened and reduced by half, about 8 minutes.
Transfer the contents of the pan to a food processor and puree until smooth. Season with salt and pepper. Return the puree to the saucepan and cook over moderate heat, stirring constantly, until warmed through. Serve at once.