Genoa Sauce

Sauce Génoise (Genoa Sauce) teaches one true thing: an emulsion preserves the texture you give it at the beginning. Pound the pistachios and pine nuts to a perfectly smooth paste before the first drop of oil, because mayonnaise can carry that silkiness, but it cannot correct grit.

The original formula assumed a saucier, a large mortar, and a quart of oil destined for a busy cold buffet. This home version keeps precisely one third of its yolks, oil, nuts, lemon, Béchamel, and herb purée, enough for a generous dinner party without leaving a basin of raw-egg sauce behind. The brigade quantity was scaffolding. The nut pounding, mayonnaise method, one-minute scald, and fine sieving are the dish, so they stay. Fir-apple kernels become pine nuts and pimpernel becomes salad burnet, their present names rather than substitutions. One cook, one stove, one evening.

Finished properly, the sauce is satiny and pale herb green, with pistachio and pine nut beneath the bright lemon and fresh herbs. It belongs beside cold poached fish, where its richness meets clean, firm flesh. Before you lift the whisk, finish pounding the nuts until no grain remains beneath the pestle. That is the step that decides the sauce.