Season halibut on both sides and dust lightly with the flour. Butter a flat casserole generously and distribute the onions, shallots and garlic evenly on the bottom of the dish. Lay the fish on top and distribute the wine, bay leaf and mushrooms around it; dot with the rest of the butter. Cover and bake at 350 degrees for 20-30 minutes, basting occasionally.

When fish is almost cooked (but not breaking-this will depend on the thickness of the filet), carefully set the fish on a platter and boil the cooking liquid down slightly for a minute or two. Add the cream and reduce a little more as needed to the correct consistency. Taste for seasoning and pour sauce over fish. Garnish with the minced parsley and serve with steamed potatoes.