We recommend buying shucked oysters for this recipe: shucking dozens of oysters can get old (and expensive). To shuck live oysters, see here.
Combine in a pot or large saucepan over medium-low heat:
Cook, stirring, until the butter is melted and the onion and celery are tender but not browned, about 7 minutes. Remove from the heat and stir in:
Set over medium heat and stir frequently. When the milk is steaming and the oysters float, add: