Oysters Stuffed a la Mornay

Poach about thirty medium oysters in their liquor, pare and split them through the center, then stuff this opening with a fine hash made of half lobster, half mushrooms and a little parsley mixed with a little bechamel sauce (No. 409), reduced until it becomes thick; garnish a buttered baking dish with these oysters, cover with a layer of cold Mornay sauce (No. 504), smooth the top nicely and strew over some grated parmesan cheese; and color in a very hot oven or under the gas salamander.