adapted by There's Always Thyme to Cook
3 large potatoes, peeled and cut into cubes (keep the cubes in a bowl of cold water until ready to use)
1 large celery root, tough outer parts removed, cut into cubes
1 cup heavy cream or half and half or milk (I used milk)
1/2 stick cold butter, cut into pats
salt, to taste
Special Equipment: food mill or a potato ricer
Place the potatoes in a large pot. Make sure to add enough water to cover vegetables by 2 inches and season generously with salt. Bring the water to a rapid boil. Add the celery root and cook until both vegetables are tender. Strain the celery root and potatoes.
Put the cream in a small saucepan and bring it to a boil. Put the celery root and potatoes through a food mill or a ricer over a large bowl. Add about the hot cream and butter. Stir until the cream and butter are thoroughly combined. Taste for seasoning. Keep warm until ready to use.