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Green Soup
2 bunches watercress 2 diced potatoes 2 hard-cooked egg-yolks 2 slices bread 2 tablespoons butter Cook the watercress until almost done, then add potatoes and cook until they are soft. Press through a sieve and add the puree to the water in which it was cooked. Brown the bread slightly in one tablespoon of the butter, and cut into small cubes. Add the minced egg-yolks and the remaining tablespoon of butter to the soup, season to taste, add the cubes of bread and serve hot.
A thin potato-and-watercress purée finished with croutons and crumbled egg yolk. The original assumes you know how much water to start with, so the main decision is left to the cook.
- The missing measurementNo quantity of cooking liquid is given. About 1 quart of water or light stock suits 2 bunches of watercress and 2 diced potatoes; the finished soup should be thin enough to drink but hold the bread cubes briefly before they sink.
- Don't overcook the cressWatercress needs only a few minutes at a simmer; longer and the green goes olive-drab and the peppery character turns flat and cabbagey. As written the cress goes in first and stays in the pot while the diced potatoes cook through, which takes considerably longer; to keep the colour you can reverse it and drop the cress in at the end.
- Sieve or blenderA food mill or blender does in seconds what the sieve was for. Blend hot with a little of the cooking water, then return to the rest; a stick blender in the pot works equally well.
- Egg yolksThe hard-cooked yolks go in at the end as enrichment and garnish (the recipe does not say whether off the heat). Push them through a fine sieve rather than mincing with a knife -- they break into a fine powder that disperses instead of clumping.
- The breadTwo slices of a firm white loaf, crusts on or off. The recipe browns the slices in a tablespoon of butter and then cuts them into small cubes, adding them to the soup before serving; passing them at the table instead keeps them from softening.
- Seasoning"season to taste" means at least salt and pepper. Watercress and potato both take more salt than seems reasonable; a squeeze of lemon at the end sharpens the green flavour that boiling dulls.
- YieldServes 4 as a first course, 2 as a light supper.
Watercress soup belongs to the French tradition of thin green purées built on potato and a leaf, of which potage cressonnière is the best-known example. The potato does the thickening, a technique that became common in French home cooking over the nineteenth century as the potato shed its reputation as fodder. Watercress itself was a commercial crop in both England and France by the mid-1800s, grown in spring-fed gravel beds and sold in bunches by street vendors, which may be why old recipes count it in bunches rather than by weight.