- Make panade first. Melt butter in a small skillet, and stir in flour. Cook a few minutes without browning the flour, then add water and a dash of salt and pepper. Stir until very thick. Pour into small bowl and set in freezer or refrigerator to get cold. But don’t let it freeze. Cook spinach and have ready to use.
- Wash turbot. Dry on paper towels. Head should be removed. Do not skin, but cut off fins and tail fin with kitchen scissors.
- With a very sharp, flexible knife, known as a fillet knife, cut down the center of the white side of the fish, along the backbone. (Use white side rather than black side; it will look nicer when served.) Make an incision, perpendicular to the first, 2 inches from the top of the fish and across to each side. The two incisions should make a cross. Carefully, with the fillet knife, cut the flesh from the backbone all the way out to the fins. Lay the fillets back so you can get at the backbone.
- Now, carefully, with a kitchen scissors cut through the backbone vertebrae, then carefully cut the flesh from the underneath side of the backbone. Do a one-inch section at a time, lifting out the bone as you go. Be careful not to cut through the underneath skin as you debone the fish for stuffing.
- Butter a large flat pan. Cut a piece of foil to the shape of the fish, then trim it ½ inch smaller. Butter it, then sprinkle with minced shallots. Lay fish on shallots, cut side up. Add wine and water to pan.
- Make quenelle mixture. Put cod fillets into blender container. Add cold panade. Blend. Add salt, 2 egg whites, and blend; if mixture looks stiff it will absorb another white, add it, then another if the mixture will hold a fourth. The size of the eggs is a determining factor as well as the moisture in the fish. It may even take 5 egg whites.
- When egg whites are all added, add crème to make a firm, but moist mixture. Add 1 tablespoon crème at a time and then more if necessary. Test the mixture by poaching ½ teaspoonful in simmering water. If it holds together, add nothing more. Taste the cooked quenelle and adjust the seasonings. If mixture seems heavy, add more crème; if it doesn’t hold together, add more egg whites. A quenelle must be light yet creamy and moist. When mixture is perfect, add the truffles.
- Dry cavity of turbot with paper towels, then fill with quenelle-panade mixture. Close fish, but do not sew. Place foil with fish, filled side up, in pan. Tear a piece of foil to fit inside the pan. Butter the foil and lay it, butter side down, over top of stuffed turbot. Bring liquid to a boil on top of the range, then put into a 425-degree oven. Oven poach about 40 minutes on the lowest shelf of the oven. (One burner under a large pan would not cook the fish evenly, so cook it in the oven.)
- Start the sauce. Melt butter in skillet, then stir in flour. Stir-cook 2 minutes, but do not brown. Remove from heat. Stir in cold cream to stop the cooking process. Mix together yolks and crème ready to use.
- When turbot is done the flesh will have lost its translucence and turned a pearl-white. Take from the oven. Discard top sheet of foil. Spoon all liquids from pan. There should be one cup or more. If there is not enough, add white wine to make at least one cup, but do not use more. Pour this into the sauce.
- Have large serving platter heated and ready to receive the fish. Tip pan on edge of platter and, using the foil under the turbot, slide fish and foil out of the pan onto the platter. Tear foil out from under the fish if it shows, otherwise leave it alone. Set into oven to keep warm while finishing sauce. Oven is off.
- Heat and stir the sauce until thickened. Finish with mixture of yolks and crème. Heat but do not boil. Remove skin from top side of turbot and surround with well-drained, buttered spinach. Then coat fish with sauce. Pour remainder of sauce into a separate dish to pass at the table. Serve quenelle stuffing with each serving of turbot, along with spinach.
Set blade of carving knife down on fins on one side and pull them away from meat. Put bones on separate plate and send to the kitchen. Cut down middle of turbot lengthwise, then crosswise through stuffing and through bottom fillet. Lift this layered piece of fish and stuffing from the bottom skin and serve. Cut one side, then remove fin bones and carve the other side.