Once the oysters have opened, put them in a strainer or colander over a bowl to catch the liquid. Discard the flat top shells but keep the deeper bottom ones. Put a layer of rock salt in an ovenproof dish large enough to hold all the oyster shells. Nestle the reserved shells into the salt. Place an oyster back into each one.

Put the shallots, oyster liquor and champagne in a saucepan and reduce by about half, depending on how much oyster liquor you have.

In a double boiler or metal or Pyrex bowl placed over a saucepan, whisk the egg yolks over barely simmering water. Slowly drizzle in the wine-oyster reduction. Beat with a whisk until everything is well mixed.

Next, beat the melted butter through it, stirring it quickly in drops. Continue whisking until the sauce thickens and lightens in both colour and texture. This can take up to 10 minutes, so be patient. You’re after a creamy mixture that is not quite as thick as a hollandaise sauce.

Season to taste with lemon juice, pepper and salt, although if the champagne is good, lemon should not be necessary.

Spoon the sauce over the oysters, then, if you wish, scatter with breadcrumbs. Put them under the grill for a minute or two, until the top has heated through again.