Purée de Crosnes, otherwise Japonaise

Purée de Crosnes, dite Japonaise (silken crosne soup with tiny tapioca pearls) teaches a severe little lesson: delicacy begins with cleanliness. Crosnes hide earth in every ring of their ivory spirals, and no amount of butter can charm grit out of a finished spoonful. Wash them until the last basin stays clear, then the rest is gentle work.

The source method assumes a tammy, a saucier free to press the vegetables through it, and boiled milk or white consommé waiting beside the stove. At home, this becomes about two quarts: the book's proportions are preserved at one and a half pounds of crosnes, three medium potatoes, three cups of first cooking liquid, and three tablespoons of perles du Japon. A food mill or brief blending followed by a fine sieve replaces the tammy, while the unspecified finishing butter is fixed at three tablespoons so the home cook isn't asked to guess. The dedicated saucier is scaffolding. The butter stewing, gentle simmer, sieving, and final mounting are the dish.

The purée should be pale ivory, softly earthy and nutty, with enough body to hold the translucent pearls without becoming mashed potato in a bowl. Keep the heat low when milk is used, and keep the machine work brief, because scorched milk and overworked potato are the two turns toward heaviness. Before any pan goes on the flame, clean every groove of every crosne. That is the step that decides the soup.