Cabillaud Crème Gratin

Cabillaud Crème Gratin (cod gratin with Mornay and a Duchesse potato border) teaches that a composed gratin is architecture before it is browning. The Mornay must stop one-third of an inch below the potato rim. Ignore that line and the sauce bubbles over the border as it colours; respect it and you get tender cod under an ivory glaze, held by a bronzed, deeply ridged crown.

The source kitchen assumed a saucier with Mornay ready, fish cooking liquor held beside the range, prepared Duchesse Potatoes (No. 221), ten portions moving through service, and a salamander waiting to colour them. The standing stockpot has no business here because the entry calls for the cod's own liquor, so that is what loosens the sauce. For four people, the original two pounds of cod becomes 13 ounces, a home broiler replaces the salamander, and the fish cooks at a bare tremble because a rolling boil would fracture a tender fillet before it reaches the dish. One cook, one stove, one evening.

Holding pans and brigade volume are scaffolding, so they go. The sturdy piped border, egg-yolk gilding, Mornay, Parmesan, butter, and immediate final glaze are the dish, so every one stays. Before you touch the fish, remember the step that decides everything: build the border thickest at its base and keep the sauce below its crest.