3: Melt 50 g butter in a small frying pan until it froths.
4: Add the chopped shallot, onion and garlic. Salt and pepper and mix well. Cook for 1 minute without colouring.
5: Pour 120 ml dry white wine into the pan, mix well and turn the heat down slightly.
6: Leave to cook gently until all there is no liquid left in the pan. Set aside.
7: Prepare 4 sprigs parsley, keeping only the leaves.
8: Put into a high-sided container: the cooked onions, parsley, salt, pepper and the juice of ½ lemon. Blend together.
9: Transfer the mixture to a bowl and add 3 tablespoons breadcrumbs and 2 tablespoons olive oil. Mix to make a thick paste, adding more breadcrumbs if necessary. Set aside.
10: Preheat the oven to 360°F (180°C). Prepare the fish fillets. Rinse and dry, then remove the skin and any remaining bones. Salt and pepper on both sides.
11: Spread the topping mixture in a fairly thin, even layer on each fillet. The best tool for this job is a palette-knife, if you have one.
14: Bake for about 15 minutes (this will depend on the thickness of your fillets) and finish under the grill to give them the important browned top.
15: Serve on hot plates and trickle a little lemon juice over just before serving.
Remarks
The breadcrumb topping can be prepared in advance as it keeps and freezes well. From this basic recipe many variations are possible: red wine instead of white, coriander or chervil instead of parsley, etc.