Shuck the oysters, preferably on a wooden chopping board that is grooved to catch juices.
Tip the liquid from the oysters into a small bowl (including any spilt during the opening procedure, but take care to strain out the shell grit).
Roughly chop the 6 least handsome oysters, and put them aside, along with any oyster scraps from the shells.
Add 3 tablespoons of olive oil to a cast-iron pan.
Cover with a lid and sweat the onion over a very slow heat until transparent.
Add the celery and continue cooking, covered, until soft.
Uncover, then stir in the rice until translucent.
Turn up the heat, add the wine and stir until nearly evaporated.
Add ground black pepper and fish stock to cover.
Reduce to medium heat, and continue cooking until the stock is absorbed or evaporated, stirring frequently.
(Once the stock is used up, continue by adding boiling water.)
Continue adding the stock one ladleful at a time until the rice is al dente (this takes about 20-25 minutes).
Check for salt and season if necessary (the stock may be quite salty so it's best to wait till this stage before seasoning).
Add the chopped oysters and oyster liquid to the risotto.
Continue cooking for a minute or so, and then remove from the heat.
Gently fold in the remaining oysters.
Serve into bowls immediately.
Sprinkle on a little zest of lemon and chopped herbs.
Take care to apportion the oysters equally among diners, though any extras should by rights go to the chef !
serves 4