Remove and discard the stalks of the mousserons and wipe off any pieces of grass or dirt but do not wash them.
Skin and fillet the Dover sole. Trim the edges and slightly flatten each fillet using the side of a heavy-bladed knife or a cutlet bat – this will prevent the fillets from curling as they cook. Fold each fillet in half; if they prove to be a little too long, then fold the tail over about 2.5 cm/1 inch and then fold in half. Lightly butter an ovenproof pan, scatter the chopped shallot over the bottom and lay the fillets in, keeping them separate. Add the fish stock and the sherry, cover with buttered greaseproof paper and set the pan over a high heat until the liquid begins to tremble. Transfer to the oven and
Place the stock over a high heat and reduce by three-quarters, then add the cream and reduce slightly until it starts to thicken.