Sauce Bercy — Shallot, Wine, and Fish Fumet Velouté

Bercy is fish velouté built on a reduction of shallots and white wine with fish fumet, finished with butter and parsley — the quintessential sauce for simply cooked fish. Named for the Bercy neighbourhood in eastern Paris, once the site of the city's great wine market, it captures the French genius for transforming a few ingredients into something greater than their sum. The reduction is the foundation. Sweat 4 finely minced shallots in butter until translucent — 3-4 minutes, no colour. Add 250ml of dry white wine (Muscadet or Chablis, something with minerality rather than fruit) and 250ml of fish fumet. Reduce by two-thirds over medium-high heat. This concentrated reduction carries the entire flavour of the finished sauce: the sweetness of the shallots, the acidity of the wine, the sea-mineral backbone of the fumet. When reduced, you should have approximately 150ml of intensely flavoured liquid. Add this reduction to 300ml of fish velouté (blonde roux plus fish fumet, simmered 20 minutes). Simmer together for 5 minutes to marry the flavours. Off heat, mount with 60g of cold butter in small pieces, swirling the pan. The butter emulsifies into the sauce, adding richness and gloss. Finish with a tablespoon of finely chopped flat-leaf parsley. The finished Bercy should be pale gold, glossy from the butter, with visible flecks of green parsley and the occasional translucent shallot piece. It should taste of wine and the sea — bright, clean, and savoury — without any trace of fish stock's sometimes murky quality. The wine reduction burns off the alcohol but concentrates the grape's acid and mineral character. Bercy belongs on simply poached or pan-fried sole, turbot, bass, or any white fish where the flesh is mild enough that the sauce can speak without shouting over the protein. It is also the base for Bercy butter (beurre Bercy), where the same reduction is beaten into softened butter and chilled — a compound butter for grilled fish.