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Cream of Leeks
Place in a saucepan four pared, cleaned and sliced leeks with one ounce butter and cook on a slow fire for ten minutes, occasionally stirring meanwhile; dredge in two ounces flour, stir well while heating for one minute, moisten with one and a half quarts broth and a quart of milk; add two branches parsley, one branch chervil and six sliced shallots, season with a level tablespoon salt, two saltspoons cayenne, a saltspoon grated nutmeg, lightly mix and let slowly boil for forty minutes. Dilute two egg yolks with a gill cream and add to the soup with a half ounce butter, mix well while heating for two minutes, strain through a sieve into a basin, then through cheesecloth into a soup tureen, and serve with a plate of bread croutons separately.
A classic French-style velouté of leeks, thickened first with a roux and finished with an egg-and-cream liaison. Nothing here is difficult, but the last two minutes decide whether it is silky or scrambled.
- The liaison must not boilOnce the yolks and cream go in, hold the soup below a simmer — around 175F. A single boil curdles the yolks and no amount of straining afterwards will hide it. Temper the yolk-cream mixture with a ladle of hot soup first, then stir it back in.
- Archaic measuresA gill is half a cup. A saltspoon is a quarter teaspoon, so the recipe wants 1/2 teaspoon cayenne and 1/4 teaspoon nutmeg. Two ounces of flour is about 1/2 cup; one ounce of butter is 2 tablespoons.
- SaltA level tablespoon of salt assumes unsalted homemade broth. With commercial stock, add a teaspoon at the start and correct at the end, after the reduction has concentrated everything.
- CayenneHalf a teaspoon in 2.5 quarts is assertive but not fiery. Start with a quarter teaspoon if you want the leeks to stay the loudest thing in the bowl.
- Cleaning leeks"Pared and cleaned" means trimming the root and the tough dark green, then splitting the leeks lengthwise and rinsing between the layers. Grit trapped in the shanks will survive forty minutes of boiling and end up in the sieve stage as sand.
- Chervil and shallotsFresh chervil is uncommon; a small handful of parsley plus a pinch of tarragon gives a close approximation of its faintly aniseed note. Six shallots is a generous quantity by modern sizing — four is closer to the intent if yours are large banana shallots.
- Don't let it "slowly boil"Forty minutes at a true boil with milk in the pot risks scorching on the bottom and a skin on top. Keep it at a bare simmer and stir the base occasionally.
- The double strainSieve first to catch the herb stems and leek fibre, then pass through damp cheesecloth for the glassy texture the original is after. A blender before straining will give a fuller-bodied soup if you prefer that to the clarified version.
- YieldRoughly 2 to 2.5 quarts before straining, depending on how much reduces in the forty minutes — eight to ten first-course servings.
Leek soup thickened with a roux and finished with yolks and cream is the standard nineteenth-century French potage aux poireaux, and the double straining through sieve and then cheesecloth suggests restaurant work rather than household cooking — plausibly the technique of a professional kitchen with staff to do the pressing. This is the French repertoire arriving in the United States through hotel dining rooms, where a soup was judged partly on whether it was perfectly smooth. The liaison of egg yolk and cream was the standard finish for a velouté before butter-mounting and blenders made it optional; it enriches and slightly thickens without further flour. Note that the leek here is treated as a delicate vegetable worth its own soup, not merely a background aromatic.