Pat scallops dry and sprinkle with 1/4 teaspoon
each of salt and
pepper (total). Heat 1 tablespoon butter in a 12-inch nonstick
skillet over medium-high heat until foam subsides, then sear
scallops, turning once, until golden brown and just cooked through,
about 5 minutes total. Transfer to a platter.
Add shallot, wine, and vinegar to skillet and boil,
brown bits, until reduced to 2 tablespoons. Add juices from platter
and if necessary boil until liquid is reduced to about 1/4 cup.
Reduce heat to low and add 3 tablespoons butter, stirring until
almost melted, then add remaining 3 tablespoons butter and swirl
until incorporated and sauce has a creamy consistency. Stir in
tarragon and salt to taste; pour sauce over scallops.