Sauce Bercy

The sauce takes its name from Bercy, the quarter on the eastern edge of Paris that for generations was the city's great wine entrepôt, where barrels arrived by river and rail to be stored and traded; a clutch of bistro dishes "à la Bercy" — sauces and garnishes leaning on white wine and shallot — carry the district's name. The classical repertoire records two: a fish Bercy, built on fish fumet and velouté for poached sole and other fish, and a meat Bercy of white wine and shallot bound with meat glace or demi-glace and finished with marrow and parsley, for grilled entrecôte. Escoffier sets both down in Le Guide Culinaire. The naming is firmly tied to the wine trade of Bercy rather than to a single chef.

Pale and lightly thickened, it tastes clean and bistro-bright: white wine cooked down to lose its rawness, a generous savour of softened shallot, and parsley and lemon keeping it fresh. On fish it is a foil rather than a blanket — enough body to cling, light enough not to smother delicate flesh. The meat Bercy eats richer, the marrow lending its buttery, mineral note. A Bercy that tastes thin and acidic has had its wine under-reduced; one that tastes only of butter has lost the shallot and herb in the cooking.

The flavour engine is the reduction of shallot, white wine and fumet: simmering drives off the wine's alcohol and harsh edge while concentrating its acidity and fruit, and the shallots soften and sweeten into the liquid. A fish velouté — a blond roux loosened with fish stock, where the starch gelatinises to thicken — gives the sauce just enough body to coat without weighing it down. The finishing butter is whisked in off the heat so it emulsifies into the warm sauce for gloss rather than melting to grease, and the parsley and lemon go in last to keep their fresh colour and aroma, which long cooking would dull. In the meat version, demi-glace replaces the velouté and poached marrow is folded in at the end.