Skin the brill fillets and trim any frill and a little off the tails to give 100 g/4 oz trimmings for the mousseline.
To make the mousseline, pour boiling water over the pistachios, leave for 30 seconds, then drain. Pull off the skins. Purée the fish trimmings with the pistachios, chervil and egg white in a processor or blender until smooth. Rub through a fine sieve. Season vigorously with salt and pepper. Gradually beat the cream into the mixture.
Spread the carrots and mushrooms on the base of a buttered flameproof dish, and lay the brill fillets on top. Either fill a piping bag fitted with a plain 1.25 cm/½ inch nozzle with the mousseline and pipe over the fillets, or spread the mousseline over the fish using a palette knife. Pour in the wine, cover with foil or a lid and cook in a
Remove the fillets to a warmed serving dish. Place the cooking dish over a direct heat, and reduce the juices by half over a fairly fast flame. Season, then whisk in the butter a few cubes at a time. Taste and adjust seasonings. Pour round the fish, garnish with chervil and serve.
© 1990 Joyce Molyneux. All rights reserved.