Sorrel Soup
(Provincial France.) This recipe comes from the country, but the homesick students can always find sorrel soup in the little restaurants of the Latin Quarter. Pick sufficient sorrel to make a pint of puree, chop it, and add 1 ounce butter; cook, stirring well, for 20 minutes. Add 1 ounce flour and press through a sieve; let it cook again, with 1 pint hot milk and 1 pint of stock; season it with salt, pepper, and nutmeg and stir in the yolks of 2 eggs. Strain it again and serve with croutons.
A classic French potage santé built on a roux, a milk-and-stock base and an egg-yolk liaison. Most of the work is in getting the sorrel down to a purée; the risk is all in the last minute.
- The hinge: never boil after the yolksOnce the yolks go in, the soup must stay below a simmer or it will curdle into threads. Temper the yolks with a ladle of hot soup first, return the mixture off the heat, and hold it around 175F.
- How much sorrelA pint of puree is a lot of leaves; expect to need on the order of a couple of pounds of trimmed sorrel, since it collapses almost to nothing the moment it meets heat.
- Twenty minutes is for the older methodTwenty minutes is long by modern practice -- Sorrel melts to a khaki puree within a few minutes in butter. The long cooking may be meant to drive off water and soften coarser leaves; with tender market sorrel, cooking only until it breaks down is enough.
- Pans and colourSorrel is high in oxalic acid. Use stainless steel or enamel rather than bare aluminium, cast iron or copper, which discolour the soup and pick up a tinny taste. The bright green will go dull olive regardless; that is normal.
- Ounces are weightOne ounce of butter is 2 tablespoons; one ounce of flour is a scant 1/4 cup. Together they make a light roux for a quart of liquid, giving a thin, drinkable soup rather than a thick one.
- Two sievingsThe first pressing is done with the flour still raw, which is awkward. It is easier to cook the roux into the purée, add the liquids, simmer, then sieve once before the yolks go in.
- StockA veal or light chicken stock suits the soup. Unsalted stock is safer here, so the seasoning can be judged at the end.
- YieldThe liquids alone come to three pints, so expect appreciably more than a quart before straining. Croutons fried in butter rather than oven-dried suit it.
- Oxalic acidSorrel in soup quantities is unremarkable, but people prone to kidney stones or on a low-oxalate diet are usually told to avoid it.
Sorrel soup, potage a l'oseille, was long a spring dish of the French countryside, made when the first sharp leaves came up and there was little else green to eat; sorrel grew wild in meadows and along hedges, so the soup cost little beyond butter, milk and a little stock. It is related to the dish that appears in French kitchen literature as potage sante, the "health soup" -- a name often linked to the idea that the sour leaf cleansed the blood after winter, though that association is tradition rather than documented etymology. The note about homesick students points to this book's audience: it belongs to a genre of Anglo-American cookery writing aimed at travellers and expatriates, promising that a dish tasted in a cheap Paris restaurant could be reproduced at home. Sorrel is uncommon in English-speaking kitchens today -- it does not ship or store well -- and it survives mainly in French, Polish, Ukrainian and Jewish cooking, where the same leaf turns up in schav.