3tablespoons extra dry (Brut) champagne taken from the bottle to be drunk with the dish (cork it up well and put in refrigerator)
6tablespoonschilled single cream
15g (½oz) butter
ahandful of seaweed
200g (7oz) coarse salt
Open the oysters and remove them carefully from their shells with ateaspoon, first cutting through the muscle that attaches them with a small sharp knife. These operations should be carried out over a strainer held over a small saucepan to catch the juices. Reserve the hollow halves of the shells. Add the 3tablespoons champagne to the small pan, adding a little pepper. Bring to the boil, then reduce over a medium heat until no more than 2tablespoons of liquid remain. Meanwhile plunge the oysters into very cold water for 15–20 seconds to firm them up, using a slotted spoon.
Pick over and trim the spinach and wash it thoroughly. Cook in a minimum of boiling salted water, uncovered, for 3–4 minutes. Refresh in cold water, drain and squeeze out the moisture. Chop coarsely with a knife.
Spread 200g (7oz) coarse salt on a gratin dish which will fit under your grill, and set the concave shells firmly in it. Dry in a low oven for 5 minutes and keep hot.
Whisk the cream until it is slightly thick and add the egg yolk. Then whisk this mixture vigorously into the champagne reduction in the small saucepan (1). Heat through, whisking all the time, and without boiling - which would coagulate the egg and ruin the sauce. When the sauce has thickened a little, remove from the heat and taste for the seasoning.
Heat the grill until it is really hot. Meanwhile, reheat the spinach (2) with a nut of butter. Then put a little spinach in each hot shell (3), place an oyster on each and cover lightly with the sauce (4). Place the gratin dish under the grill until the sauce has formed a golden skin.
Make nests of seaweed on two large plates and plant six shells on each. Serve very hot.