Coquilles Saint-Jacques à la Parisienne

Coquilles Saint-Jacques takes its name from the scallop, the shell long worn as the emblem of pilgrims to Santiago de Compostela. The gratin in its shell is a classic of the codified repertoire, and Escoffier's Le Guide Culinaire (1903) lists several treatments under the name. The à la parisienne style names the bourgeois restaurant rendering — scallops in a Mornay sauce, framed by a piped border of duchesse potato and gratinéed — as distinct from the Breton coastal version finished plainly with butter and crumbs. Mornay sauce itself, a béchamel enriched with Gruyère and egg yolk, is a 19th-century Parisian creation of the haute-cuisine kitchen, and the dish belongs squarely to that white-sauce tradition.

Crack through the cheese-crusted top and the sauce underneath is pale gold and just-set, holding plump scallops and slippery mushrooms in a Gruyère-rich cream. The scallops are barely cooked — sweet, springy, faintly briny — so the contrast is soft seafood against a savoury, browned crust. The piped potato border has gone crisp at its ridges and stays soft beneath. Each shell is a single rich portion; the empty fluted shell, scraped clean of sauce, is half the pleasure. A squeeze of lemon cuts the cream if the kitchen is generous with the cheese.

Scallop muscle is delicate and cooks in moments; held too long it turns rubbery and weeps water, so it is poached only until opaque in the wine, then folded into the finished sauce rather than baked through. The wine poaching liquor is reduced and stirred back into the Mornay so nothing of the shellfish is lost. The sauce is a béchamel — a white roux of butter and flour cooked without colour, loosened with milk — finished with grated Gruyère and a yolk; the cheese must be stirred in off the heat or below a simmer, since boiling a Gruyère sauce breaks the proteins into a stringy, oily mess. Under the salamander the exposed cheese and cream brown by Maillard reaction in two or three minutes, the brief blast setting the crust without overcooking the scallops sealed beneath.