Coquilles St.-Jacques

1-1/2 Pound medium sea scallops (24 to 28),
1/4 cup dry vermouth
1-1/2 tablespoons minced shallot
1-1/2 tablespoons white-wine vinegar
1-1/2 tablespoons dry white wine
1 tablespoon cold water
9 tablespoons cold unsalted butter, cut into tablespoon pieces
1-1/2 teaspoons finely chopped fresh tarragon
Marinate scallops in vermouth 15 minutes.
Make beurre blanc: Simmer shallot in vinegar and wine in a small heavy
saucepan until liquid is reduced to about 1 tablespoon. Remove from heat and add water. Reduce heat to low and cook, whisking in 6 tablespoons butter 1 tablespoon at a time, adding each new piece before previous one
has melted completely and occasionally lifting pan from heat to cool mixture. (Sauce must not get hot enough to liquefy; it should be the consistency of a thin hollandaise.) Remove from heat and whisk in tarragon and salt and pepper to taste. Keep warm off heat, covered.
Cook scallops: Drain scallops and pat dry between paper towels. Heat 1 1/2 tablespoons of remaining butter in a 12-inch nonstick skillet over
moderately high heat until foam subsides. While butter is heating, season
half of scallops with salt and pepper. Saute scallops, turning once, until
just cooked through, about 4 minutes total. Wipe out skillet and saute
remaining scallops in remaining 1 1/2 tablespoons butter in same manner.
Serve scallops with beurre blanc.