1 celery root (celeriac–1 lb.), trimmed, peeled, cut into 1/2-inch pieces
1 lb. parsnips, trimmed, peeled, cut into 1/2-inch pieces
1 lb. potatoes, peeled, cut into 1-inch pieces
1 cup milk
1 tablespoon butter

Cook celery root and parsnips in large pot of boiling salted water until beginning to soften, about 10 minutes. Add potatoes; cover and cook until all vegetables are tender, about 20 minutes longer. Drain well. Transfer vegetables to processor. Add milk; puree until almost smooth. Return puree to same pot; stir over medium heat until heated through. Season with salt and pepper. Mix in butter. Transfer to bowl. Serve.

(from Bon Appétit, January 1998)