How to Make It
Place the celery root and potato in a medium saucepan and cover with cold water. Season with salt and cook until soft, 15 to 20 minutes.
Drain the water and return the celery root and potato to the pan. Pour in the cream and simmer over medium heat, stirring occasionally to prevent sticking, until most of the cream has been absorbed, about 10 minutes.
Remove from the heat, stir in the butter and season with salt and pepper. Puree the celery root and potato and any liquid in a food mill, return to the pan and keep warm over simmering water until serving time.
Recipe courtesy of Wolfgang Puck, Adventures in the Kitchen, Random House, 1991.