Filets de Poisson Gratinés, à la Parisienne [Fish Filets Poached in White Wine; Cream and Egg Yolk Sauce]
In the following recipe, the fish poaching liquid is cooked with a flour and butter roux to make a fish velouté. The velouté is then combined with cream and egg yolks to produce a delicious, velvety sauce called a parisienne. Although it uses almost the same elements as the sauce Bercy, because of its cooked roux and its egg yolks, sauce parisienne is far more subtle in taste and texture. It is the basis for all the great fish sauces described later. When the sauce is to be used for a gratin, as in this recipe, the whole dish may be prepared ahead of time, and reheated later. Before the fish is sauced, it may be surrounded with various cooked shellfish as suggested at the end of the recipe. Serve with this a chilled white Burgundy, or an excellent white Graves.
Poach the fish in white wine as described in the master recipe. Drain the poaching liquid into an enameled saucepan and rapidly boil it down until it has reduced to 1 cup.
Melt the butter, blend in the flour, and cook slowly, stirring, until they foam and froth together for 2 minutes without coloring. Off heat, beat in the boiling liquid, then the milk. Boil, stirring, for 1 minute. Sauce will be very thick.
Blend the yolks and cream in the mixing bowl. Beat in driblets of hot sauce until a cup has been added. Beat in the rest of the hot sauce in a thin stream. Return the sauce to the pan. Set over moderately high heat and stir with wooden spoon, reaching all over the bottom of the pan, until the sauce comes to the boil. Boil and stir for 1 minute. Thin out with additional spoonfuls of cream until the sauce coats the spoon nicely. Season carefully to taste with salt, pepper, and drops of lemon juice. Strain.
Spoon the sauce over the fish. Sprinkle with cheese, and dot with butter.
(*) If not to be served immediately, set aside.
Just before serving, reheat slowly almost to simmer on top of the stove. Run under hot broiler to brown the top of the sauce.