Remove skin and bones. Cut salmon into strips 1/2 inch thick by 1 1/2 inches wide and up to 8 inches long.
Butter 8 custard cups and coil salmon into the cups. In a double boiler, cook mushrooms and onion juice for 5 minutes then add the flour, light cream, salt, pepper, cayenne and mace and stir constantly until cooked and thick.
Pour sauce into custard cups then bake at 375/F for 25 minutes.
Drain off juice from cups, unsold the fish and place in an ovenproof dish.
Sprinkle with the buttered crumbs, put a buttered mushroom cap on each fish roll.
Broil the rolls until the mushrooms are done and the crumbs browned.