(Proportions are for 18–24 persons.) Clean a 5–6 lb fish, such as pike, zander, or salmon, and cut along the spine to take out the backbone. Add salt, remove the other bones, and stuff as follows:
Finely chop 3 lbs of boneless fish. Place in a mortar and add 1½ French rolls soaked in milk and squeezed out, 2½ spoons butter, 10 allspice, salt (2 finely chopped onions fried in 1 spoon butter), ½ nutmeg, and 6–10 eggs. Pound everything together and rub the mixture through a sieve with a wooden spoon. Stuff the fish, sew it up, and place it on a roasting pan greased with 1 spoon butter. Sprinkle with salt and finely chopped parsley, onion, and leek. Pour over ½ to 1 glass rich bouillon and cover with a clean cloth, folded in two and soaked in rich bouillon. Roast the fish in the oven, basting it frequently with that same sauce.
When the fish has cooked, remove it, brush it off, and let it cool. Arrange the fish on an oblong platter and decorate with mousse, colored aspic, and other decorations, as indicated in the Remarks.
Serve with Provençal sauce, mixed sauce, or mustard sauce.