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