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Potage Aux Herbes Lie
Remove stems from a quart fresh sorrel, carefully wash and thoroughly drain on a sieve. Pick green leaves from two heads fresh lettuce, wash and drain, then cut both sorrel and lettuce in julienne strips, place in a saucepan with two branches each finely sliced parsley and chervil, an ounce butter, and gently cook for ten minutes, frequently stirring meanwhile. Pour in two and a half quarts broth, season with a teaspoon salt, half teaspoon each pepper and sugar, lightly mix and let slowly boil for one hour. Mix on a plate a gill cream, an egg yolk, juice of a quarter lemon and add to soup. Mix well while heating five minutes, pour soup into a tureen and serve with six slices toasted French bread separately.
A classic French herb soup finished with a cream-and-yolk liaison — the lié of the title. Everything else is straightforward; the finish is where it can fail.
- The hinge: never boil after the yolk goes inOnce the cream, yolk and lemon are stirred in, hold the soup below a simmer — around 170-180F — for those five minutes. A boil will curdle the yolk into threads, and the acid from the sorrel and lemon makes it curdle more readily than it would in a plain broth.
- A gillHalf a cup, four fluid ounces. Temper it: whisk a ladle of hot soup into the cream-and-yolk mixture on the plate before returning it all to the pan.
- A quart of sorrelMeasured as loose leaves, which wilts down to very little; the equivalent weight varies a great deal with how tightly the leaves are packed. If your market sells sorrel in small bunches you may need three or four. Spinach plus extra lemon is the usual substitute, but it will not taste the same — sorrel's sourness is the point of the dish.
- ChervilRarely stocked and short-lived once cut. Flat-leaf parsley with a pinch of tarragon or a few fennel fronds approximates the faint anise note; skip it rather than substitute dill.
- Pan materialSorrel is high in oxalic acid and will pick up a metallic taste and grey colour from bare cast iron or unlined aluminium. Use stainless, enamelled cast iron or a lined copper pan.
- The hour-long boilModern practice would cut this to 20-30 minutes, which is ample for the greens and keeps the broth fresher. Long boiling may have served to reduce and concentrate a homemade stock; with commercial broth you mostly lose flavour. If you do simmer an hour, expect to have lost volume and to need more liquid.
- BrothThe recipe says only 'broth'; a light chicken or veal broth suits. If using boxed stock, hold back on the teaspoon of salt until the end and season to taste, since a homemade stock may well have been less salty than a commercial one.
- Yield and serviceThe six slices of toast tell you it serves six, at about a cup and a half each as a first course. Serve the toast alongside, not floating, so it stays crisp.
Potage aux herbes lié is the bound, or thickened, version of the plain French herb soup — lié refers to the liaison of egg yolk and cream stirred in off the boil, a technique Escoffier's generation codified but which is far older in French kitchen practice. Sorrel (oseille) was a kitchen-garden staple across northern Europe long before lemons were cheap, valued precisely for the sourness that oxalic acid gives its leaves; it appears in French soups, sauces for shad and salmon, and purées far more often than in English cooking, where it is often said to have fallen out of favour in the nineteenth century. Its place in The International Cook Book (first published in 1906, with later printings), Filippini's survey of national dishes for American households, reflects the era's assumption that a well-run kitchen could produce a proper French potage, and that a cook would know what sorrel was — an assumption a modern shopper may find optimistic.