SOLE À LA DIEPPOISE [Fish Filets with Mussels and Shrimp]
Arrange the poached fish filets on a lightly buttered serving platter and surround them with the mussels and shrimp. Just before serving, cover the platter and reheat the fish for a few minutes over simmering water. Drain off any accumulated liquid before napping the fish with the following sauce:
Following the technique for sauce parisienne, cook the flour and butter slowly together until they foam and froth for 2 minutes. Off heat, beat in the hot fish cooking liquid, then the milk. Boil 1 minute. Beat the hot sauce by droplets into the yolks and cream. Return mixture to saucepan and boil, stirring, for 1 minute. Thin out with more cream if necessary, and correct seasoning. Strain. Film top of sauce with a tablespoon of melted butter if not to be served immediately.
Just before serving the fish, bring the sauce to the simmer. Then remove it from heat and beat in the butter 1 tablespoon at a time.
Immediately spoon the sauce over the hot fish and shellfish. Decorate with the shrimp and truffles and serve.