Pour into a saucepan one pint of white wine; add a tablespoonful of vinegar, two well chopped shallots, also the quarter of one bay leaf, two stalks of chives, two sprigs of thyme, and four branches of chervil; reduce the whole thoroughly, and then add to it one pint of veloute sauce (No. 415), a little cayenne pepper, and some spinach green; strain through a tammy, incorporate a few pieces of good butter and serve.
A classic hot green sauce built on velouté, coloured at the end with spinach extract. Two things decide whether it works: how far the wine is reduced, and how gently the sauce is treated once the green goes in.
Sauce verte covers two quite different things in nineteenth-century French cooking: the cold mayonnaise-based green sauce for salmon, and this hot one, a velouté tinted and perfumed with fresh herbs. Vert d'épinards, the pressed chlorophyll extract, was among the colourings professional kitchens kept on hand, alongside caramel for brown and cochineal for red. Charles Ranhofer, chef at Delmonico's in New York across some three decades, published The Epicurean in 1894 as a working record of that kitchen, and his sauce chapters are organised the way a brigade worked: a handful of mother sauces given full recipes, then dozens of derivatives like this one that consist of a flavouring reduction plus a cross-reference. The cross-references are not laziness but the structure of the trade.