Piquante Sauce

A brown-roux sauce sharpened with vinegar and chopped pickles, in the classic piquante mould. The ingredient list as printed is incomplete, so the base needs reconstructing before you start.

• The missing quantitiesThe list gives only the garnish and the vinegar, yet the method calls for butter, flour and stock. A workable reconstruction is about 2 tablespoons butter, 2 tablespoons flour and 1 to 1 1/2 cups brown stock, which suits the tablespoon-scale garnish.
• Brown the butter, then the flourThis is the hinge. The roux must be cooked to a genuine nut-brown before any liquid goes in, or the sauce tastes of raw flour and looks muddy rather than deep brown. Keep the heat moderate and stir constantly; browned flour thickens less than pale flour, so the sauce stays loose.
• "Chopped pepper"Most likely a sweet green pepper, chopped fine, rather than ground black pepper; the tablespoon measure and its place among the other chopped garnishes point that way, though the recipe does not specify.
• Pickle and capersThe recipe does not say which pickle; a sour cucumber pickle suits the sauce best, and cornichons work well. Drain the capers rather than adding their brine, since the vinegar already supplies the acid.
• The vinegar reductionSimmering the aromatics in vinegar for five minutes drives off the harshest edge of the acid and softens the pepper. Cider or white wine vinegar suits it; distilled white vinegar will read sharper.
• Stock quality decides the sauceWith so little else in it, the sauce is only as good as the brown stock. A well-reduced beef or veal stock is worth the trouble; a thin commercial broth will need reducing first or the twenty-minute simmer will not save it.
• Yield and servingOn the reconstruction above it makes roughly a cup and a half; the recipe itself gives no yield. It belongs with plain roast or boiled beef, tongue, pork or leftover meats reheated in it, where the acid cuts the fat.