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Leek Soup Au Gratin
Thoroughly wash four fresh, medium leeks, finely slice them, then place in saucepan with one ounce butter and fry for twelve minutes, or till a nice light brown. Sprinkle in two tablespoons flour, mix well while heating for one minute, moisten with two quarts broth and a pint water, season with a teaspoon salt, half teaspoon pepper, mix well and let boil for forty-five minutes. Transfer soup into an earthen soup tureen, arrange six slices toasted French bread over soup, sprinkle one and a half ounces grated Parmesan cheese over bread, set in oven for fifteen minutes, remove and serve.
A leek version of the gratinéed onion soup, and it works on the same principle: a long, slow browning of the allium first, then a crust of bread and cheese finished in the oven. Two things need translating — the oven temperature, which the original omits entirely, and the vessel, which must be ovenproof.
- Brown the leeks properlyThe twelve minutes in butter is the hinge. Leeks scorch easily, so keep the heat moderate and stir; you want an even light brown, not blackened edges, which will turn the whole pot bitter.
- Wash them like you mean itGrit hides between the layers near the pale green. Slice first, then rinse the slices in a bowl of water and lift them out, leaving the sand behind — washing whole leeks rarely gets it all.
- Oven temperatureNone is given. A moderate oven, 350–375°F, for the fifteen minutes will melt and lightly colour the Parmesan. If you want a browned crust, finish under the broiler for a minute or two instead.
- The tureenAn "earthen soup tureen" here means a glazed stoneware or earthenware vessel that can go into the oven. Some modern porcelain tureens are decorative only and may crack, so check before using one. Use a Dutch oven, individual onion-soup crocks, or any ovenproof casserole.
- Liquid quantitiesTwo quarts broth plus a pint of water is 2.5 quarts — generous for four leeks. Expect a thin, brothy soup; the flour gives body rather than thickness. Reduce the water if you prefer it more concentrated.
- BrothThe recipe's "broth" would have come from the household stockpot, often beef or veal. Beef stock gives the closest result to the classic gratinée; chicken stock makes it lighter and more clearly a leek soup.
- Cheese and breadOne and a half ounces of Parmesan across six slices is roughly half a cup grated — a light dusting rather than a lid. Use a dried or oven-toasted baguette; fresh bread collapses into the broth before the cheese sets.
- YieldSix slices of bread points to six servings. Season at the end as well as the start — forty-five minutes of boiling concentrates the broth, and a salted stock plus the given teaspoon of salt can easily overshoot.
Leeks are among the oldest cultivated alliums in Europe, and leek-and-broth soups run through French provincial cooking long before onion soup gained its Parisian reputation. The gratin finish here — bread laid over the surface, cheese scattered on, the whole set in the oven until the top sets — is the same technique as soupe à l'oignon gratinée, and the word gratin refers to the crust itself rather than to any particular dish. The International Cook Book was compiled by Alexander Filippini, long associated with Delmonico's in New York, and it reflects an American appetite for continental cooking presented as a tour. A recipe like this one sat comfortably in that project: cheap ingredients, French bread, Parmesan, and a name that told a diner exactly which country the plate was meant to have come from.