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Onion Soup (Spanish)
Peel and slice 3 large Spanish onions; separate them into rings and fry in a tablespoonful of butter until tender and slightly browned. Put them in a saucepan, add 2 quarts of water, and boil an hour; season to taste with salt and pepper. Crumble the inside of a stale roll, sift and add to the soup, and boil for an hour longer. When just ready to serve, add the yolks of 2 eggs, beaten light, and mixed with 2 tablespoonfuls of vinegar and a few spoonfuls of the soup, pouring in gradually and stirring briskly one way. Pour into the tureen, and serve at once.
A frugal water-based onion soup thickened with bread and finished with an egg-and-vinegar liaison. The finish is the whole dish, and it is the one step that can fail.
- The liaison is the hingePull the pan off the heat before adding the yolk mixture, and keep the soup below a simmer afterwards. Boiling it, even briefly, will scramble the yolks into threads and leave the broth grainy.
- Temper the eggs properly"A few spoonfuls of the soup" means enough hot liquid to warm the yolks before they go into the pot; add it a spoonful at a time while whisking. Stirring "one way" is period advice with no chemistry behind it, but steady constant motion does matter.
- Spanish onionsThe large, mild, straw-skinned onion sold as Spanish or sweet onion. Three large ones is roughly 2 to 2 1/2 lb; a stronger yellow cooking onion will make a much sharper soup than intended.
- Two hours of boilingTwo quarts of water boiled uncovered for two hours will reduce by a third or more. Either cover the pan partway or keep a kettle of hot water nearby to top it back up, or you will finish with a thick porridge.
- The bread thickener"Crumble the inside of a stale roll, sift" means rubbing the soft crumb through a coarse sieve to break it into fine, even crumbs — about 1 cup from a dinner roll. A food processor does much the same job. The crumbs dissolve into the broth and, with the yolks, give the soup what body it has.
- Water, not stockThe recipe uses water rather than stock, so it leans on butter, long boiling and vinegar for flavour. It works, but a light chicken or vegetable stock in place of the water gives a rounder result.
- VinegarTwo tablespoonfuls; a wine or sherry vinegar suits the dish. Add it to the yolks as written rather than to the pot, so it goes in diluted and evenly distributed.
- ButterOne tablespoonful for over two pounds of onions is scant. Two to three tablespoons will brown them more evenly without scorching, and adds the fat the broth otherwise lacks.
- YieldAbout 6 cups after reduction — four servings as a first course. Serve immediately; the egg-thickened broth does not reheat well.
Bread-thickened onion soups belong to the older European tradition of the panada and its relatives, where stale bread rather than flour or cream gave a soup its body — an economy dish built from onions, bread and water. Egg-yolk-and-acid finishes of this kind appear widely in Iberian and Mediterranean cooking and in French sauce poulette: yolks for richness, acid to lift a broth made without meat. Recipes like this circulated in American compilations under national labels, and the "Spanish" here may refer as much to the large mild onion as to any specific Spanish original.