Use a kettle with lid. Select tubers of uniform size; wash; do not cut or break the skins. Put them in boiling water, and continue boiling until, when you pierce one with a fork, you find it just a little hard in the center. Drain by raising the cover only a trifle when kettle is tilted, so as to keep in as much steam as possible. Hang the kettle high over the fire, cover closely, and let steam ten minutes.