Mussels, back at their best, can be as useful as truffles in perfuming fish dishes. Take neat one-portion fillets of any white or flat fish and arrange on buttered greaseproof paper or foil with very fine slivers of onion or leeks and other vegetables such as fennel, carrot and tomato. Add a leaf or two of suitable fresh herbs, seasoning and as few as two, well scrubbed, de-bearded raw mussels in their shells. Seal the paper, making a tight seam but allowing plenty of room inside the packets. Bake on a metal sheet in a hot oven for up to 15 minutes. Cut open the packets at table. The mussels will have opened and their fragrant liquor permeated the whole dish.