In a bowl, mix the mirin, soy and rice wine vinegar with the diced eschallot and ginger.
Bring water in a steamer to the boil and steam the oysters on a plate for 3 minutes or until just heated through.
If you prefer a more cooked oyster, then cook for 5 to 6 minutes.
Remove the oysters from the steamer and arrange them on a service platter.
Pour the sauce evenly over the oysters and sprinkle with the finely sliced green shallots.
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