Mousse Chaude d’Éperlans à la Royale

Ingredients

Equipment Needed

• •1-quart (950 ml) metal charlotte mould or smooth-sided heatproof pudding basin
• •Food processor with metal blade
• •Parchment paper
• •Rolling pin or flat meat pounder
• •Small offset spatula
• •Deep roasting tin for the bain-marie
• •Instant-read thermometer
• •Small sharp knife
• •Clean pastry brush
• •Warm serving platter and sauceboat

Instructions

1. 1

   Chill and divide fish

   Put the food-processor bowl and blade, a metal mixing bowl, and the cream in the cold for at least 15 minutes. Pat the smelt fillets dry and keep them over a bowl of ice. Weigh 8 oz (225 g) for the forcemeat, remove its skin, and cut it into 1-inch pieces. Reserve about 2½ oz (75 g) for the inner layers and the remaining 10½ oz (300 g) of the broadest, most even fillets for lining the mould.

2. 2

   Prepare mould and fillets

   Reserve 1 teaspoon of the butter for the mushroom. Butter the bottom and sides of a 1-quart mould. Cut a parchment circle for the bottom and a collar for the sides, press them into place, then butter their exposed surfaces. Lay the lining fillets between two sheets of parchment and flatten them very lightly with a rolling pin, just enough to break their fibres without crushing the flesh. Trim them to even widths and lengths, saving the trimmings for the inner layers. Cut the truffle strips about one-quarter as wide as the fillets.

3. 3

   Make the mousseline

   Process the skinned smelt with the salt until it becomes smooth and tacky, about 30 seconds, then add the egg white and white pepper. Process briefly until absorbed. Add all but 1 tablespoon of the ice-cold cream in four additions, pulsing only until each disappears and scraping the bowl between additions. Poach a teaspoon of forcemeat in barely trembling water for 2 minutes; it should be tender, cohesive, and delicately seasoned. Pulse in the final tablespoon of cream. If the mixture becomes warm, shiny, or oily, stop immediately, spread it in the chilled metal bowl, and set the bowl over ice for 10 minutes before adding the remaining cream. Ça se rattrape. Do not add crumbs or flour, which would save the shape by sacrificing the dish.

   Keep the forcemeat below 50°F (10°C). Friction from the processor is the danger, so short pulses and cold pauses matter more than speed.
4. 4

   Line the mould

   Arrange smelt fillets across the bottom of the mould with their skin sides against the buttered paper, fitting a narrow truffle strip between each one. Line the sides in the same fashion, placing the fillets on a diagonal rather than upright and keeping every skin side against the mould. Patch any small gaps with trimming pieces. The pattern need not look perfect from inside; unmoulding reverses it, and the silver skin and black truffle will read clearly on the plate.

5. 5

   Build the layers

   Spread mousseline forcemeat ½ inch (1.25 cm) thick over the lined bottom and sides, using a small wet spatula and taking care not to disturb the pattern. Cover the bottom with a close layer of truffle slices, then spread over a thin layer of forcemeat. Lay reserved smelt fillets and anchovy fillets alternately across it. Cover with more forcemeat, add another layer of truffle slices, and continue until the mould is filled to within ½ inch (1.25 cm) of the rim. Finish with an even layer of forcemeat. Tap the mould once against a folded towel to settle hidden air pockets, then cover it with buttered parchment and foil.

6. 6

   Poach very gently

   Heat the oven to 325°F (165°C). Set the covered mould in a deep roasting tin and pour hot water around it to come halfway up the sides. Poach for 45 to 50 minutes. The water should quiver but never boil; if bubbles gather around the mould, lower the oven and add a little cool water to the bath, because hard heat makes the mousseline grainy and forces out its moisture. Insert a thin knife into the centre at 45 minutes. The mousse is set when the blade comes out clean and hot, or the centre registers at least 145°F (63°C). If the blade carries raw paste, continue in 5-minute intervals.

7. 7

   Prepare the mushroom

   While the mousse finishes, make the champignon cannelé (fluted mushroom). With a small sharp knife, cut eight shallow curved channels from the centre of the mushroom cap toward its rim. Put the cap in a small pan with the reserved teaspoon of butter, cover, and cook over low heat for 3 to 4 minutes, until tender but still pale. Keep it warm.

8. 8

   Drain and unmould

   Warm the serving platter. Remove the mould from its bath, discard the covers, place the platter over it, and invert at once. Raise one edge of the mould about ⅛ inch (3 mm) with the tip of a palette knife and leave it for 2 minutes so the liquid collected inside can drain. Blot that liquid from the platter, lift off the mould, and peel away the paper. If white froth clings to the smelt fillets, remove it with a clean pastry brush dipped in warm water. Brush, never wipe, or the patterned fillets may tear.

9. 9

   Finish sauce and serve

   Reserve 2 tablespoons of Mousseline Sauce (No. 92). Off the heat, fold the softened crayfish butter into the remaining warm sauce in small pieces until its colour is evenly coral-ivory. If butter sits in beads, set the bowl over barely warm water for 5 seconds and continue folding. If the sauce thins or looks greasy, move the bowl over cool water and fold in the reserved sauce one spoonful at a time. Ça se rattrape. Spoon enough sauce around the mousse to form a generous pool, set the fluted mushroom on top, and send the remainder in a warm sauceboat. Cut with a thin knife dipped in hot water between slices. À table!

Chef Tips

• •Choose smelt with bright silver skin, firm flesh, and a clean cucumber-like scent. Ask the fishmonger to leave the skin on the fillets, because that skin forms the visible silver pattern when the mousse is unmoulded.
• •The source permits sole, salmon, or trout when smelt cannot be found. Sole gives the closest pale delicacy, trout is fuller, and salmon changes both the colour and flavour; each makes a proper variation, but none is Mousse Chaude d’Éperlans.
• •A whole preserved black truffle is the honest classical pantry answer when fresh truffles are out of season. It gives real slices and dark visible strips. Scented oil cannot make the pattern or the texture, so it has no work here.
• •The mould must be completely lined and well buttered. A pudding basin can replace a charlotte mould if its sides are smooth and its capacity is close to 1 quart, but avoid a ridged vessel, which catches the fish during unmoulding.
• •Serve with a dry, mineral white wine such as Chablis or Muscadet. The mousse is rich with cream and crayfish butter, so the wine should bring freshness rather than more weight.
• •Refrigerate leftovers within 2 hours and keep them for no more than 1 day. Reheat individual slices, covered, in a gentle water bath; direct oven heat dries the exposed mousseline.

Advance Preparation

• •The smelt can be filleted, pin-boned, and divided 1 day ahead. Keep it tightly covered over a tray of ice in the cold, changing the ice if it melts.
• •The filled mould can be assembled up to 4 hours ahead and refrigerated, tightly covered. Let it stand at room temperature for 15 minutes before poaching, or expect the cooking to take an additional 5 to 10 minutes.
• •Prepare the truffle strips, truffle slices, and crayfish butter a day ahead. Keep the truffle covered in the cold and bring the crayfish butter to a soft, spreadable consistency before finishing the sauce.
• •Mousseline Sauce (No. 92) must be made close to serving because its whipped-cream finish dislikes a long wait. Have every other element ready before preparing it, then hold it according to its own recipe until the mousse is unmoulded.

Frequently Asked Questions

Nutrition Information

1 serving (about 325g)