Caper Sauce
2 tablespoons butter 2 tablespoons flour 1 cup meat broth 1 teaspoon onion juice 1/2 teaspoon salt Dash of pepper 1 tablespoon capers Melt the butter; add the flour, then the broth and seasoning, stirring to prevent lumps. When it boils, add the capers; stand over hot water for ten minutes and serve.
A standard blond roux sauce, thin enough to coat rather than cling. It comes together in under fifteen minutes and needs no adjustment beyond a little attention to the broth.
- The hinge: cook the roux before the liquidMelt the butter and let the flour bubble in it for a minute or two before the broth goes in, or the sauce will taste of raw flour. It should smell faintly nutty but stay pale.
- Meat brothThe recipe specifies nothing beyond 'meat broth'; sauces of this kind were commonly made with the liquor from the meat being served. Unsalted or low-sodium stock is the right substitute, since the recipe already adds half a teaspoon of salt and the capers bring more.
- Onion juiceA period shortcut: onion grated on a fine rasp and the juice squeezed out through cloth, giving flavor without visible pieces. A quarter of a small onion yields about a teaspoon; a microplane works, or use a pinch of onion powder.
- CapersA tablespoon is restrained by current taste. Rinse brined capers if they are very salty. The recipe adds them as the sauce boils, immediately before it goes over hot water, so they need only warm through.
- Stand over hot waterThis means a double boiler or a bowl set over a pan of barely simmering water. It holds the sauce at serving temperature without letting it reduce, scorch, or break while the meat is carved.
- ConsistencyTwo tablespoons each of butter and flour to one cup of liquid gives a medium sauce, one that coats a spoon. Loosen it with a splash more broth if it tightens during the ten-minute hold.
- YieldAbout one cup, enough for four to six servings alongside boiled or roasted lamb, mutton, or poached fish.
Caper sauce belongs to the long English tradition of serving boiled mutton with something sharp to cut the fat, and by the nineteenth century it was so fixed a pairing that cookbooks often listed the two together as a single dish. The capers themselves are the unopened flower buds of Capparis spinosa, a Mediterranean shrub; they reached northern kitchens pickled in brine or vinegar, which made them an acidic, shelf-stable seasoning available year-round before refrigeration. The construction here—butter and flour cooked together, then let down with stock—is the roux-based white sauce that anchored American cooking-school teaching around the turn of the twentieth century, where a student learned one base and then a dozen variations on it. The instruction to hold the finished sauce over hot water reflects a kitchen without a warming drawer or a low-simmer burner, where a pan of water offered gentle, indirect heat.