Caper Sauce
2 Tablespoons Butter 2 Tablespoons Barley Flour 1 Tablespoon Cornstarch 2 Cups Milk 1 Teaspoon Vinegar 3 Tablespoons Capers Salt and Pepper to Taste Rub butter, flour and cornstarch to a paste. Add the milk and stir over moderate fire till it thickens. Add vinegar, capers and seasoning. Serve with lamb or mutton.
A white sauce thinned with caper brine rather than a true caper butter. The method is a cold paste rather than a cooked roux, so the one thing worth changing is how long you cook the thickened sauce.
- Cook out the starchRubbing raw flour and cornstarch into butter and adding cold milk works, but the sauce tastes pasty if you stop the moment it thickens. Keep it at a bare simmer for another 3-4 minutes, stirring, before the vinegar goes in.
- Barley flourOften used as a wheat-saving substitute during the First World War, though it appears in other contexts too. It thickens less strongly than wheat flour and tastes faintly nutty; plain all-purpose flour at the same quantity gives a cleaner result, in which case the cornstarch can be dropped.
- "Moderate fire"Medium heat on a modern burner, and lower once it begins to thicken. Milk sauces catch on the bottom of a thin pan; use something heavy and a flat-edged wooden spoon or a whisk.
- Add the acid last, off the heatAdd the acid last -- the recipe puts the vinegar in after the sauce has thickened, and that order is worth keeping. Vinegar stirred into hot milk before it has thickened can curdle it, and hard boiling after the vinegar goes in can split the sauce.
- Capers and their brineThree tablespoons drained is a generous amount for two cups of sauce. A tablespoon of the caper brine can replace the vinegar and gives more flavor; if using salt-packed capers, rinse them and keep the vinegar.
- SeasoningSalt cautiously at the end. Capers and their liquid are already salty, and the sauce reduces slightly as it cooks.
- YieldAbout two cups, enough for six to eight servings alongside a leg of lamb. It thickens as it cools and can be loosened with a little hot milk.
Caper sauce with boiled mutton is one of the fixtures of nineteenth-century English cookery, and it crossed into American books as well: the sharp, salty buds cut the fat of the meat much as mint jelly does. Capers are the unopened flower buds of Capparis spinosa, a Mediterranean shrub, pickled in vinegar or packed in salt. What may date this particular version is the barley flour. Wheat was heavily conserved for export during the First World War, and household cookbooks of that period substituted barley, rye, oat and corn flours, sometimes propping them up with a little cornstarch for thickening power, as here.