Fry two tablespoonfuls of chopped onions in two ounces of butter, lay in the mackerel cut up into four ounce slices and when well fried, moisten with water, add a garnished bunch of parsley and salt and let the fish cook; when ready to serve add cooked peas (No. 2742); finish by thickening with a little veloute sauce (No. 415), egg-yolks and butter. Dress the fish, pour the peas over and serve.
Ranhofer writes for a brigade that already has velouté and cooked peas standing by, so the recipe reads as a series of reminders rather than a method. Two things need spelling out: how much liquid, and how to handle the egg-yolk finish.
Charles Ranhofer's The Epicurean (1894) records the kitchen of Delmonico's in New York, where he cooked for over thirty years, and its mackerel chapter shows how thoroughly a French brigade could work an American fish. Spanish mackerel, an Atlantic coastal species landed in quantity from the Chesapeake south, was a fashionable market fish in the second half of the nineteenth century, prized as milder and firmer than the common mackerel, and Ranhofer gives it a run of treatments borrowed straight from French repertory: with gooseberries, stuffed, and here aux petits pois, the classic spring garnish. The finish with velouté, egg yolks and butter is the old sauce poulette family, a liaison used across French cooking for poached fish, veal and mushrooms; its presence in a mackerel dish is a reminder that in this book the fish is the local element and the technique is entirely imported.