Cover the fish carcasses well with cold water, bring slowly to a boil, skim off all the gray scum that rises to the surface, add the remaining ingredients, except for the white wine, and simmer, the lid slightly ajar, for about 15 minutes. Add the white wine, return to a boil, and continue to cook, lid ajar, at a simmer for another 20 minutes. Pour the contents into a large sieve, straining thoroughly, but without pressure, and reduce the liquid over a medium-high flame by about one third. Set aside the cup necessary for the panade and refrigerate the remaining fumet until the following day.
Stew the chopped onion in butter, over very low heat, stirring occasionally, for 20 or 25 minutes, until soft and slightly yellowed. Then add the mushrooms (which have been chopped or put through the Mouli-juliènne only the moment before) and seasonings, turn the flame up, and toss regularly until the mushrooms have lost all their water and the mixture has returned to a dry, firm consistency, stir in the chopped parsley, cook for another minute or so over a low flame, remove from the heat, and stir in a few drops of lemon juice.
Boil the cupful of fumet with the breadcrumbs, stirring vigorously with a wooden spoon, until reduced to a consistent, fairly stiff paste.
When the duxelles and the panade are sufficiently cooled to be handled, combine them with all the remaining ingredients of the forcemeat, except for the salmon cubes, working them together with your hands. Then mix in—gently, so as not to break them up—the cubes of salmon flesh.
Soak the sole filets for a few minutes in ice-cold water, spread them out on paper toweling, sponge them gently dry and press each firmly, but without violence, with the side of a large knife blade to slightly flatten it out. Make several shallow incisions diagonally on the skin side of each filet with a sharp knife. Line a generously buttered, rectangular, 2-quart terrine (the bottom and sides, but not the ends) with the filets, slightly overlapping, the flesh side pressed into place against the buttered sides of the terrine, the skin side visible, the tips of the filets hanging over the edges of the terrine sides, and spoon in the forcemeat, spreading it evenly and mounding the surface. Rap the bottom of the terrine smartly several times against a towel-muffled tabletop to settle the contents and fold the filet tips, one by one, over the surface of the forcemeat (depending on the proportions of the terrine, they may or may not completely enclose the forcemeat; if not, several filets should be halved at a sharp bias and pressed into place to complete the enclosure, their tips tucked down inside those of the other filets, against the body of the forcemeat, before the other tips are folded into place).
Press a sheet of buttered parchment paper or aluminum foil over the surface, cover with the lid, and cook in a bain-marie (using a fairly deep container, which should contain enough hot, but not boiling, water to immerse the terrine by three quarters) in a medium oven (about 350° to 375°) for approximately 45 minutes, or until the surface of the terrine is firm and springy to the touch. Leave to cool until only tepid and unmold, first placing a pastry grill over the surface and turning it and the terrine upside down as if to unmold the contents (this is in order to drain off loose liquid) and turning it right side up again after draining, before unmolding onto the serving platter. Press plastic wrap over the entire surface to protect it from contact with air and refrigerate until the following day.
The fish fumet, depending on the varieties of fish used in its confection, will be more or less lightly jelled and the sediment will have settled to the bottom of the bowl. Carefully remove all traces of fat from the surface of the fumet and from the sides of the bowl and spoon the lightly jelled fumet—only that part which is limpid (about two thirds) into a saucepan. (It may be clarified by whisking it with beaten egg whites until a boil is reached and simmering it for a quarter of an hour before straining it through a tightly woven towel but (1) clarification tends to somewhat emasculate the jelly; (2) there should be enough limpid fumet without having recourse to clarification; and (3) the troubled fumet remaining in the bottom of the bowl is perfectly good for the confection of a fish sauce for another preparation.) Dissolve the gelatin in a small amount of warmed fumet in a small saucepan, heat it, stirring, until a boil is reached, and incorporate it into the remainder, also first warmed. Test it for firmness by placing a spoonful in a small container (metal will take faster) in the coldest part of the refrigerator for 10 minutes or so (or on cracked ice in the refrigerator); it should be fairly firm in view of the fact that sherry will be added to it. Taste the jelly for salt and, when it is only barely tepid, stir in the sherry, adding it in two or three doses and tasting before adding more—its presence should not be aggressive.
Stew the tomatoes, salted, and herbs over a low flame, stirring to prevent sticking, until all superfluous liquid is evaporated. Pass through a fine sieve, leave to cool, stir in the pepper and lemon juice and mix thoroughly with the cream, which has been first whipped until nearly stiff. Taste for seasoning.
Copyright © 1974 by Richard Olney. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.