Scale and fillet the sea bass. Remove the few small bones at the head end of each fillet with a pair of pliers. Wash the watercress well and remove any yellowing leaves and roots. Season each fillet with salt and freshly ground white pepper. Bring the fish stock and the white wine to the boil over a high heat, place the fish in a steaming basket over this and steam. When the fish is cooked – it should take 3-4 minutes – remove it from over the stock and keep warm.
Reduce the fish stock until only about 4 tablespoons remain. Add the chives and the cream and bring back to the boil.