Prepare a puff paste with one pound each of flour and butter and one ounce of salt. Roll the paste out to a thickness of about three-fourths of an inch, and cut it round to the size of the dish on which it is to be served. Place the flat of paste on a baking sheet, brush it over with beaten egg, and cut a circle through the middle about one-fourth of an inch deep, leaving an edge about one inch wide all round. Bake the paste in a moderate oven, and when cooked lift up the center piece which will have risen; scoop out the uncooked paste, brush the inside with beaten egg, and place it in an oven for five minutes longer. Prepare a filling of scalloped fillets of soles, mussels, oysters and sliced mushrooms. Mix the cooking liquor of the mussels with some lean veloute sauce, boil it until somewhat reduced, then thicken it with the beaten yolks of two eggs. Mix the sauce with the garnishing, place the cover of paste on, stand it on the dish it was made to fit, and serve.