Fresh cod, whiting, hake, turbot, gurnard, all white fish cooked in a well flavored court bouillon make a shell more or less fine depending on the quality of the fish. Trim the fish, cooked in the court bouillon, completely. Cut into dice. Thinly slice the mushrooms, sprinkle with the lemon juice to keep white. Finely chop the shallots, gently fry in butter, add the mushrooms. When their water has evaporated, sprinkle with the two level tablespoons of flour. Stir while cooking for 2 minutes, moisten with the cream and the same quantity of sieved court bouillon or white wine. Cook gently for 15 minutes. Salt, pepper, add a pinch of nutmeg. Remove from the heat, add the egg yolks thinned with a few drops of lemon juice, add the fish. Fill the shells, lightly sprinkle with the bread crumbs mixed with the cheese. Bake in a hot oven, serve very hot and slightly browned. If you add mussels, count 4 or 5 mussels per shell, open them (without using their water) and discard their shells, add at the same time with the fish.
