Shuck the oysters, keeping the deep half shells. Put them in a casserole with their liquor and set over a low flame until the liquid whitens. Remove the oysters from the pan with a slotted spoon and keep warm.
Add to the casserole the fish stock, Champagne, and truffle juice, then cook to reduce by a third. Stir in the cream and reduce again until you have a rich sauce the color of ivor