Put fish through food chopper, using finest blade or whirl a small amount at a time in a blender.
Put fish in a bowl set in a pan of ice water.
Slowly stir in egg whites; beat with a wire whisk to keep mixture smooth.
Stir in cream very slowly.
Add salt and pepper.
Season to taste with cayenne, ground nutmeg, or celery salt and the onion juice.
Let stand for 1 hour.
Pour mixture into a well-buttered 1 1/2-quart mold or into individual timbale molds.
Set in a pan of hot water 1 inch deep.
Cover with foil.
Bake in preheated moderate oven (350°F.) until firm.