Presoak a clay pot, top and bottom, in water for 15 minutes.
Put the halibut in the presoaked pot; add the parsley, bay leaves, onion slices, lemon, olive oil, white wine, salt, and pepper.
Cover the pot and place it in a cold oven.
Set the oven temperature at 480 degrees. Cook for 10 minutes for each inch of halibut thickness, plus 15 minutes for the pot. (Don't overcook!) When done, remove the pot from the oven and pour off the liquid into a saucepan. Heat to boiling.
Meanwhile, in a separate pan, saute the sliced mushrooms and chopped onion in the butter along with the anchovy paste, then add to the halibut sauce. Add the arrowroot and stir until thickened. Pour over the fish and serve.
© 1974 All rights reserved. Published by Echo Point.