Serve these as an appetiser and you may as well forget the main course!
half a small onion
3 egg yolks
tsp olive oil
Preheat the grill.
Shuck the oysters and remove from the shells, draining and reserving the liquid from inside the oysters.
Wash the leeks and cut into thin slices. Peel and finely dice the onion.
Heat a large cooking pot or saucepan. Add the olive and then sweat the leeks with a pinch of salt. Add the liquid from the oysters and cook 10 minutes. Add the chopped onion, champagne and the water to a saucepan. Cover and cook over a high heat until the vongole have opened. Drain the juice and then reduce by half. Place a spoonful of leeks in each oyster shell and then place an oyster on top.
In a bowl over a bain-marie, beat the egg yolks into the mixture and when it starts to thicken, remove from the heat and whisk vigorously.
Cover each oyster with the sabayon and then cook under the grill for 2 minutes.
Serve immediately with the rest of the bottle of Champagne!