This recipe can easily be made with boneless fish filets, which would make the dish easier to eat. On the other hand, whole or sliced fish make for a much more succulent sauce.
Have your fish monger clean and scale your fish.
Pre-heat oven to 350ºF (175ºC).
Wash fish well and pat dry using a paper towel.
Put all remaining ingredients in a bowl and mix well.
Place half the onions in a large, cast iron pot.
Place the fish on top. Put some of the onions into the cavity of each fish and cover the fish with the remaining onions.
Put the un-covered cast iron pot in the oven and cook until the fish has cooked in its’ juices (30 to 40 minutes).
Remove from the oven and let rest for 15 minutes before serving. Garnish with fresh herbs at the last minute.