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Mustard Sauce
Put two ounces of butter in a saucepan over the fire and warm without browning it. Mix in well two tablespoonfuls of flour, pour in gradually one pint of hot stock or water, and stir until it thickens and is perfectly smooth. Add two ounces more of butter in small pieces, stir well and sprinkle with a little salt and pepper. Mix in three tablespoonfuls of made English mustard and a little cayenne and it is ready for use.
A plain white roux sauce finished with mustard and cold butter. Nothing here is obsolete, but two of the quantities need reading carefully before you commit.
- "Made English mustard"This means mustard powder mixed to a paste with cold water, not a jarred American or Dijon condiment. Mustard powder stirred with water and left ten minutes to develop heat is the sense intended; three tablespoonfuls of it is aggressive by modern taste, so add half, taste, and go on from there.
- Weights and volumesTwo ounces of butter is 4 tablespoons (half a stick), and the recipe calls for that twice, four ounces in total. A pint is 2 cups. The finished quantity is roughly 2 cups of sauce, enough for eight servings alongside meat or fish.
- Never let the mustard boilThe mustard goes in at the very end; better still, take the pan off the heat first, though Oscar does not say to. Heating a mustard sauce after the mustard is added drives off the volatile compounds that carry the pungency and leaves a flat sauce. The same is true if you reheat leftovers hard.
- Cook the roux brieflyButter and flour want a minute or two of gentle cooking before the liquid goes in, just enough to lose the raw-flour taste without taking on color. "Without browning" is the whole instruction: any color here shows through the pale sauce.
- Adding the liquidHot stock poured in gradually with steady stirring is the reliable route. If it does go lumpy, a whisk or a quick pass through a sieve fixes it; the sauce should coat a spoon and no more, since it thickens as it stands.
- The second butterThe last four tablespoons, worked in in small pieces as the recipe directs, are what give the sauce gloss and body; adding them cold and off direct heat is the safer modern route. Do not let it boil after that point or the emulsion breaks and the butter pools out.
- Stock or waterWater works but tastes thin. Use whatever stock matches the dish, and note that commercial broth is far saltier than a hotel kitchen's own stock, so salt at the end rather than the beginning.
- What to serve it withOscar gives no pairing. This is the classic sauce for boiled beef, boiled or grilled tongue, ham, pork, and oily fish such as herring, mackerel and grilled bluefish.
Mustard sauce in this form is a plain white sauce, what Escoffier's generation classed as a velouté, brought up sharp at the end with mustard, and it was a familiar accompaniment to boiled meats and oily fish. The specification of English mustard matters: unlike Dijon, which is worked with wine or verjuice, English mustard is sold as dry flour of mustard and mixed with cold water at the moment of use, which triggers the enzyme reaction that produces its fierce, short-lived heat. That is why the powder is mixed to a paste separately and stirred in last rather than simmered with the sauce. Oscar Tschirky, the Waldorf's maître d'hôtel from 1893, compiled his very large book of kitchen formulas in 1896, and entries like this one are less inventions than the working shorthand of an American hotel kitchen operating on French lines, with sauces built from a roux, a stock and a single defining flavor.