Purée de Crosnes, otherwise Japonaise

Ingredients

Equipment Needed

• •Large bowl and clean tea towel for cleaning the crosnes
• •Soft vegetable brush
• •Heavy 4-quart saucepan
• •Small saucepan for the perles du Japon
• •Fine-disk food mill or immersion blender
• •Fine-mesh sieve and sturdy ladle

Instructions

1. 1

   Clean every spiral

   Rinse the crosnes in a large bowl of cold water, lifting them out rather than pouring the dirty water over them again. Spread them on a clean tea towel, scatter over the coarse salt, fold the towel around them, and rub briskly for 1 to 2 minutes; the salt scours their thin skins and reaches into the rings. Rinse in several changes of water, brushing any stubborn grooves individually. Stop only when the final water remains completely clear. Grit is the one fault no later technique can rescue.

   Do not peel crosnes with a knife. Their spirals make that misery, and the salted-towel rubbing removes the papery surface without wasting the little tubers.
2. 2

   Parboil the crosnes

   Bring a generous saucepan of water to a full boil. If using milk for the soup, season the water with ½ teaspoon of the fine salt; if using an already seasoned consommé, hold the salt until the end. Add the crosnes and parboil for 5 minutes from the moment the water returns to a boil. Drain thoroughly. They should have lost their raw edge but still resist the point of a knife.

3. 3

   Stew in butter

   Melt 3 tablespoons of the butter in a heavy 4-quart saucepan over medium-low heat. Add the drained crosnes, turn them until every spiral gleams, then cover and stew gently for 8 to 10 minutes, shaking the pan occasionally. Keep them pale. This is stewing, not sautéing, and browned butter would overwhelm the crosnes' quiet, nutty flavor.

4. 4

   Moisten and simmer

   Pour in 3 cups of the hot milk or white consommé, then add the minced potatoes. If using milk, add another ½ teaspoon of fine salt; with consommé, taste before adding any. Bring the soup only to a bare simmer, cover slightly ajar, and cook for 25 to 30 minutes, stirring along the pan floor every few minutes, until a crosne crushes readily and the potato has completely softened. Milk must never boil hard. If it catches, do not scrape the scorched bottom. Pour the unburned soup into a clean saucepan and continue gently. Ça se rattrape.

5. 5

   Poach the pearls

   While the vegetables cook, bring 1½ cups of the remaining milk or consommé to the barest simmer in a small saucepan. Rain in the perles du Japon while stirring, then poach gently for 15 to 20 minutes, or until nearly translucent with only a tiny white point at each center. Stir often so they remain separate. If they begin to clump, loosen them at once with a spoonful of the remaining hot liquid and stir gently. Drain through a fine sieve and keep them moistened with a tablespoon of their cooking liquid.

6. 6

   Purée and sieve

   Pass the soup through the fine disk of a food mill. If using an immersion blender, blend only until the vegetables lose their shape, then stop; prolonged blending makes the potato elastic and pasty. Press the purée through a fine-mesh sieve with the back of a ladle, leaving the fibrous fragments behind. This is the home equivalent of the tammy, and it must stay. A crosne purée that has not been sieved may taste right, but it will never have the intended silk.

7. 7

   Dépouiller the purée

   Return the sieved purée to a clean saucepan and dépouiller it, meaning hold it at a whispering simmer for about 5 minutes while skimming away any foam that gathers on top. Stir frequently. Loosen it a tablespoon at a time with the remaining hot milk or consommé until it falls from the ladle in a broad ribbon, retaining 2 tablespoons of liquid for the finish. If it becomes too thin, simmer it uncovered until the potato restores its body. Taste and add only as much remaining salt as it needs.

8. 8

   Mount and serve

   Take the saucepan off the heat. Monter au beurre, finish by whisking in the remaining 3 tablespoons of cold butter a small piece at a time, until the purée has a quiet gloss and rounded flavor. Do not boil it afterward. If butter beads appear on the surface, whisk in 1 tablespoon of the reserved hot liquid away from the heat until the emulsion returns. Divide the perles du Japon among warmed soup plates and ladle the purée around them, leaving a few pearls visible at each center. Serve at once. À table!

Chef Tips

• •Choose crosnes that are firm, pale ivory, and crisp under light pressure. Deep browning, shriveling, or softness means they have been sitting too long; purée hides their shape, but it cannot restore their fresh, faintly artichoke-like flavor.
• •The source gives two distinct soups. Whole milk produces the maigre, or meatless, version, gentle and softly sweet; white consommé makes a more savory potage with greater depth. Use one throughout, including for poaching the pearls, rather than muddling the two.
• •Do not replace the milk with cream. Potato already supplies the liaison, the binding body, and cream would make the soup heavy while muting the crosnes. Milk, potato, and butter are sufficient. Cooking well is not cooking fancy.
• •Small pearl tapioca is essential here. Large dessert pearls take too long to cook, dominate each spoonful, and lose the delicate contrast the source intends.
• •To reheat, keep the purée over low heat and stir from the bottom. If it tightens in the cold, loosen it with hot milk or consommé. Never let it boil after the finishing butter has been incorporated.

Advance Preparation

• •The crosnes may be cleaned up to 4 hours ahead. Keep them submerged in cold water, then drain and dry them thoroughly before parboiling; a wet tuber dilutes the butter instead of stewing in it.
• •The soup may be cooked, puréed, sieved, and chilled up to 1 day ahead. Reheat it gently, then dépouiller and mount it with the cold butter shortly before serving.
• •Poach the perles du Japon close to serving time. They continue absorbing liquid as they stand and become heavy if left overnight.

Frequently Asked Questions

Nutrition Information

1 serving (about 250g)