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Potage St. Sulpice
Place in a saucepan one and a half pounds fresh heads or whitefish bones and a sliced carrot and leek, two sliced branches celery, two each parsley roots, bay leaves and cloves. Moisten with three quarts water, season with two teaspoons salt, set on fire and let gently boil for forty-five minutes. Finely slice two medium, white onions, place them in saucepan with one ounce butter and fry for ten minutes, stirring once in a while; add two ounces flour, stir well with wooden spoon while heating for two minutes, then strain fish broth through a cloth over the onions in this pan and sharply mix with whisk until it comes to a boil, then let boil for thirty minutes, frequently mixing meanwhile; pour in one gill milk and a half gill cream, season with two saltspoons cayenne and one saltspoon grated nutmeg, lightly mix and boil for five minutes. Dilute an egg yolk on a plate with a tablespoon cream and the juice of half a sound lemon, add to soup, mixing while cooking for two minutes, but do not allow to boil. Remove, strain potage through Chinese strainer into a soup tureen and serve with a plate of bread croutons separately.
A classical fish velouté finished with an egg-yolk liaison. The whole thing hinges on the last step: once the yolk goes in, the soup must never boil again.
- The liaisonTemper the yolk-cream-lemon mixture with a ladle of hot soup before adding it, then hold the pot below a simmer. Boiling curdles the yolk into visible threads, and the lemon juice makes curdling more likely, not less.
- Gills and saltspoonsA gill is 1/2 cup, so a half gill is 1/4 cup. A saltspoon is about 1/4 teaspoon, which makes the cayenne roughly 1/2 teaspoon — assertive for two quarts of soup. Add half, taste at the end, and adjust.
- "Set on fire"Filippini's usual phrase for setting the pan over heat, not for flaming anything. Bring it up gently and skim the grey scum off the fish stock as it rises.
- Fish for the stock"Fresh heads or whitefish bones" most likely means the frames of lean white fish — cod, hake, sole, halibut — though in an American book of this date it may also refer to the freshwater whitefish. Lean white frames are the safer choice; strongly oily fish such as salmon and mackerel muddy the broth. Gills and any blood are best removed or the stock goes bitter.
- Cooking time for the brothForty-five minutes is longer than current practice; fish frames are usually reckoned to give most of what they have in 20 to 30 minutes, and longer boiling is often said to bring out a gluey, faintly bitter edge. You can strain at 25 minutes and reduce afterward if you want more concentration.
- Parsley rootsHamburg-type parsley root, still sold in Central European and some farmers' markets. A small parsnip plus a handful of parsley stems is the closest ordinary substitute.
- The roux stageTwo ounces flour to one ounce butter is a lean, dry roux; cook it the stated two minutes without colouring, then add the hot strained broth off the heat and whisk smooth before returning it to the fire. The half-hour simmer is there to cook out the flour taste, so keep whisking the bottom.
- Chinese strainerA chinois — the conical fine-mesh strainer. A fine sieve lined with damp muslin does the same job. Straining after the yolk goes in catches any slight coagulation.
- YieldThree quarts of water reduces to roughly two quarts of finished soup: six to eight first-course servings.
The recipe comes from Alexander Filippini's The International Cook Book, and its title follows a convention of the nineteenth-century French repertoire in which garnished soups took the names of places, patrons and institutions — Crécy, a town in Picardy, for the carrot purée; Saint-Germain for the split-pea, often traced to the Comte de Saint-Germain as much as to the Paris quarter; Saint-Sulpice for the church and square on the Left Bank. The names usually record fashion rather than origin, and no single kitchen can be credited with a soup like this one. What it does record is technique: a fish fumet drawn from heads and frames, thickened with a blond roux into a velouté, enriched with milk and cream, and pulled together at the end with a yolk-and-lemon liaison. That sequence is the backbone of dozens of fish soups in the classical canon.