Cabillaud Crème Gratin

Ingredients

Equipment Needed

• •Wide, shallow saucepan with lid
• •10 by 7-inch (25 by 18 cm) oval ovenproof gratin dish
• •16-inch (40 cm) piping bag
• •½-inch (12 mm) grooved piping tip
• •Pastry brush
• •Broad fish spatula
• •Rimmed baking sheet

Instructions

1. 1

   Poach the cod

   Bring the water and salt to a boil in a wide, shallow saucepan, then immediately lower the heat until the liquid barely trembles. Slide in the cod and poach gently for 5 to 7 minutes, depending on its thickness, until the flesh is just opaque and reaches about 140°F (60°C) at the centre. The source calls this boiled cod, but boiling describes the cooking liquor, not a command to batter the fish with bubbles. Lift the cod onto a warm plate, remove every trace of skin and bone, and divide it into small, generous pieces. Moisten with ¼ cup (60 ml / 60 g) of the cooking liquor, cover, and keep warm for no longer than 15 minutes.

   If the cod begins separating before you can lift it, slide a broad spatula underneath and move it in one piece. Broken fish still tastes fine, but small flakes disappear into the sauce; keep the pieces large enough to remain themselves.
2. 2

   Ready the glaze

   Set an oven rack about 6 inches (15 cm) below the broiler and heat the broiler to high. Warm the Mornay sauce over low heat until it flows slowly from a spoon while still coating it thickly. If it has tightened while standing, whisk in the reserved cod cooking liquor 1 tablespoon (15 ml / 15 g) at a time. Stop as soon as it loosens; a thin Mornay cannot support the gratin. If you add too much, simmer the sauce gently until it coats the spoon again. Ça se rattrape.

3. 3

   Pipe the border

   Fit a piping bag with a large grooved tip and fill it with the warm Duchesse Potatoes (No. 221). Pipe a continuous border around the inside edge of a 10 by 7-inch (25 by 18 cm) oval gratin dish, building it about 1½ inches (4 cm) high and deliberately thicker at the base than at the crest. The broad foot holds back the sauce; a narrow decorative rope will not. If the border slumps, scrape it back into the bag, let the potatoes cool for 5 to 10 minutes, and pipe again. Gild the ridges, meaning brush them lightly with the beaten egg yolk, taking care not to leave puddles between them.

   Hold the piping bag nearly upright and move steadily. Perfect symmetry is unnecessary, but the border must have no gaps, especially at the corners of an oval dish.
4. 4

   Arrange the cod

   Spoon 3 tablespoons (45 ml / 47 g) of the warm Mornay sauce over the bare centre of the dish, keeping it away from the gilded border. Drain the cod pieces well and arrange them closely over this first layer, distributing the thicker pieces around the outside and the smaller ones toward the centre. Handle them gently. You want distinct pieces of fish beneath the sauce, not a cod paste.

5. 5

   Control the sauce

   Cover the cod with the remaining Mornay sauce, guiding it between the pieces without pressing them down. Stop when the sauce stands one-third of an inch (8 mm) below the top of the potato border. This is the governing line of the dish: the Mornay expands as it heats, and anything above it will flood the ridges. If the level is too high, spoon away the excess now. Ça se rattrape before the broiler, not after. Sprinkle the Parmesan evenly over the sauce, then trickle the melted butter across the cheese and the inner edge of the potatoes.

   Judge the sauce level all the way around the dish. A low spot in the potato border becomes the path the Mornay takes when it bubbles.
6. 6

   Glaze and serve

   Set the gratin on a rimmed baking sheet and place it beneath the broiler for 4 to 7 minutes, rotating once, until the Mornay bubbles at its inner edge, the Parmesan is butter-gold, and every ridge of the border is evenly bronzed. The cod should reach 145°F (63°C) at the centre. If one section colours too quickly, shield only that patch with a small piece of foil and continue glazing the rest. Bring the dish straight to the table the moment it leaves the oven; the proud border softens if it waits. À table!

Chef Tips

• •Choose one thick centre-cut cod fillet rather than several thin tail pieces. Even thickness gives you large, tender pieces after poaching, while thin ends turn dry during the final glaze.
• •The Mornay should nap the spoon, meaning leave it evenly coated when lifted. A sauce that pours like cream will run through the fish and climb the border; a sauce that drops heavily in lumps needs a little cod liquor.
• •The source also permits the same treatment for other boiled fish, including turbot, brill, bass, and salmon. Keep the method unchanged, but adjust the first cooking so the fish is only just done before it meets the broiler.
• •Use real butter in the finish and real cream and butter in the prepared components. Margarine gives no proper gilding and leaves the sauce tasting of retreat. We don't apologize for butter.
• •Pour a dry Chablis or another firm, mineral white with enough acidity to meet the Mornay. The gratin needs freshness in the glass, not sweetness.

Advance Preparation

• •The Mornay sauce may be prepared up to 2 days ahead, covered directly on its surface, and chilled. Reheat it over low heat, whisking steadily, and loosen it with reserved cod cooking liquor only as needed.
• •Prepare the Duchesse Potatoes (No. 221) up to 4 hours ahead and keep them covered in the cold. Rewarm them gently over a low bain-marie just until pipeable; overheating makes the border slack.
• •For a dinner party, pipe and gild the border up to 1 hour ahead and refrigerate the dish. Keep the cod and Mornay separate, then warm, assemble, and glaze immediately before serving. A filled gratin waits poorly because the sauce begins softening the potato border.

Frequently Asked Questions

Nutrition Information

1 serving (about 305g)