Cut mushrooms into wedges, fry in medium skillet with 3 oz butter until golden in color. Add salt, pepper and parsley.
Pour heavy cream and mustard into skillet and lower heat. Let simmer for 5-10 minutes to reduce the sauce.
Season fish with salt and pepper, place in greased baking dish. Sprinkle 3/4 of the cheese on top of the fish and then pour the creamed mushroom sauce on top. Top with the remaining cheese and place in the oven.
Bake for about 30 minutes if fish is frozen, slightly less if fresh. Fish will be done if it flakes apart easily.
Nutrition: serves 6; calories 740; 9gm net carbs; 40gm protein.