Sprinkle the shallots or onions and the parsley over the bottom of a generously buttered, shallow baking dish, then add wine and fumet or clam juice.
Lightly salt and pepper both sides of the fillets, and set over ingredients in baking dish (they can be placed side by side, slightly overlapping, or folded in three).
Sprinkle with lemon juice and dot with butter.
Cook uncovered in a 350°F (180°C) oven 20 minutes, basting twice with pan liquid, then broil a few seconds to brown here and there.
This is good surrounded by small boiled potatoes.
Garnish all with parsley and serve immediately.