Fillet, skin and trim the John Dory. Separate each fillet into its three natural sections. Blanch the tomatoes, skin and deseed them. Cut the flesh into 5 mm/¼ inch dice and reserve. Finely snip the chives, reserving 8-12 nice lengths as garnish.
Bring the fish stock and the white wine to the boil in a saucepan and reduce the liquid by at least three-quarters. Add the cream and the grated ginger, return to the boil and reduce until it starts to thicken.