Clean and wash the salsify and cook it au blanc—that is, in water with a little flour and a drop of vinegar. When it is soft, cut it in pieces about three inches long, and prepare the sauce, which is a Béchamel sauce, smooth and rather thin, into which you put the salsify for a few minutes over a slow fire, then a yolk of egg mixed with lemon juice. Mix well, cook a minute or two without bringing to the boil, and serve at once. The amount of lemon juice is rather a question of taste. Some people prefer wine vinegar.