Scale and fillet the bass. Remove the few small bones that run from the head to halfway down the length of each fillet using a pair of pliers. Skin each fillet.
Discard the very outer leaves of the lettuces and remove the larger leaves so that only the hearts are left. Wash the leaves well, then plunge them into boiling water for a minute to blanch. Refresh in iced water and drain.
Open all of the oysters over a bowl to catch the juices and remove them from their shells; be sure to reserve any juice there may be. Reserve 8 whole oysters and cut the rest into 5 mm/¼-inch dice.
Remove the central rib from each lettuce leaf, season the fillets and wrap them in the lettuce; it will take three or four leaves to wrap each fillet. Lightly butter a shallow ovenproof pan or tray and sprinkle with the shallots. Lay the fillets of fish in the pan, add the fish stock and the white wine and cover with buttered paper or foil. Set the tray over a high heat until the liquid just starts to tremble, then transfer to the
Return the stock to a high heat. Strain any juice from the oysters through muslin into the stock and return to the boil. Add the whole oysters and simmer for 30 seconds, then remove the oysters and keep warm with the fish. Reduce the stock until syrupy, then add the cream and bring back to the boil.