In a small saucepan combine the shallots, wine, salt, and vinegar. Bring to a boil and cook until the liquid has been reduced to about 2 tablespoons.
Remove the pan from the heat and cool slightly. The liquid should be warm enough to incorporate the butter but not hot enough to liquefy it.
Whisk the butter, 1 piece at a time, into the wine mixture until the mixture is well blended and creamy. If the mixture becomes too cool and the butter will not incorporate, return the pan to a low flame for 1 to 2 minutes. Do not melt butter.
Top oysters with a dollop of butter. Serve immediately.
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