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Potage St. Germain
(France.) Cook 1 quart fresh peas in water to cover, with some parsley, 1 leek, and 1/2 ounce butter, added. Press all through a sieve. Stir in 1 pint of hot stock, chicken or veal, with yolks of 2 eggs, pepper, salt, and a little nutmeg. Add 1/2 a teaspoonful of sugar and 1 cup of boiling cream.
A classic French green pea velouté, thickened with egg yolks rather than flour. Almost everything hinges on the last step.
- Do not boil after the yolks go inOnce the yolks are stirred in, the soup is a custard and will curdle if it simmers. Temper the yolks with a ladle of the hot liquid first, return them to the pan, and hold the soup below about 180F, stirring, until it thickens slightly.
- "1 quart fresh peas" is ambiguousThe book does not say whether that is shelled peas or peas in the pod. A quart of shelled peas is well over a pound and gives a substantial soup; a quart of unshelled pods yields only a fraction of that. Read it as shelled unless you want a very thin potage.
- Frozen peas workFrozen peas are picked and blanched at their sweetest and are arguably closer to fresh garden peas than most supermarket fresh peas. Cook them only until tender, three or four minutes, to keep the colour.
- Butter and cream measuresHalf an ounce of butter is one tablespoon. The cup of boiling cream is scalded, not reduced; heavy cream gives the richness intended, light cream or half-and-half a thinner result.
- The sieve"Press all through a sieve" was the usual route to a smooth purée in a period kitchen. A blender does it in seconds, but pass the result through a fine strainer anyway to catch pea skins; removing them is what gives this soup its velvet texture.
- The leek and parsleyUse the white and pale green of one leek, well washed, and a small handful of parsley stems and leaves. Both are cooked with the peas and puréed in, not fished out.
- SeasoningThe half teaspoon of sugar may simply follow the French habit of sugaring peas, or serve to lift peas past their first sweetness; taste before adding it. Nutmeg should be barely detectable, a few scrapes at most.
- YieldAbout five cups, serving four as a first course. It is best served immediately; reheating risks breaking the egg liaison.
The name is generally traced to Saint-Germain-en-Laye, west of Paris, whose market gardens supplied the capital with peas, and in classical French kitchen language Saint-Germain came to mean simply "with peas" — potage, purée and garnish alike. Fresh green pea soup of this kind was a spring and early summer dish, tied to the few weeks when peas came in young and sweet, and it was distinguished from the split pea soups eaten the rest of the year. The thickening with egg yolks and cream is a liaison, one of the older French methods. Its appearance in a book of foreign recipes for English-speaking cooks reflects the period's assumption that a well-run household should be able to produce a French soup by name.