Matelote is the classic river-fish sauce of inland France — a rich, dark red wine preparation traditionally served with freshwater species like eel, pike, carp, and perch in the great matelote stews of Alsace, Burgundy, and the Loire. The sauce begins not with stock but with the braising liquid of the fish itself: the fish pieces are briefly flambéed in brandy, then simmered in red wine (Burgundy or Alsatian Pinot Noir) with onions, a bouquet garni, and mushroom trimmings. The fish is removed when just cooked, and the braising liquid becomes the sauce through vigorous reduction by two-thirds. This concentrated wine-fish liquid is thickened with a beurre manié (kneaded butter and flour) whisked in gradually, which gives the sauce a velvety body without the need for a pre-made roux. The garnish is the same as for all classical matelotes: pearl onions glacés à brun (browned and glazed), button mushrooms sautéed in butter, heart-shaped croûtons fried in clarified butter, and lardons of blanched bacon. This garnish is so specific that it has its own name — garniture matelote — and it defines the dish. The finished sauce should be deep burgundy, glossy from the butter, and taste of concentrated wine, fish, and the subtle sweetness of the glazed onions. Matelote is river cooking elevated to restaurant standard.
Build the sauce from the fish braising liquid — the wine and fish cook together. Reduce by two-thirds for concentration. Thicken with beurre manié — kneaded butter and flour whisked in. Garniture matelote: pearl onions, mushrooms, croûtons, lardons. Red wine — Burgundy or Pinot Noir, full-bodied but not overly tannic.
Flambé the fish in Cognac before adding the wine — this caramelises surface sugars and removes any muddy river-fish taste. The pearl onions benefit from being glacéd separately: cook in butter, sugar, and a splash of red wine until glazed and tender — they should gleam. If eel is part of the matelote, skin it and cut into 5cm tronçons — its high fat content enriches the sauce as it braises.
Using a delicate white wine — matelote requires red wine's body and colour. Under-reducing the braising liquid — thin, watery sauce without intensity. Adding too much beurre manié at once — creates lumps that are difficult to dissolve. Using ocean fish — matelote is a freshwater tradition; the fattiness of river fish supports the heavy sauce.
Escoffier, Le Guide Culinaire; Larousse Gastronomique