This classic French butter sauce makes a simple and elegant finish to poached fish and seafood. This recipe is adapted from Martha Stewart Living. Also try: Lobsters with Beurre Blanc and Sliced Broiled Scallops on the Half Shell with Beurre Blanc
In small saucepan, combine shallots, wine, and vinegar. Bring to a boil, reduce heat to medium, and simmer until liquid is reduced to 2 tablespoons, about 10 minutes.
Turn down heat to lowest possible flame. Whisk in butter, 1 tablespoon at a time, adding a piece as previous one melts. Don't allow sauce to become too hot. For a more smooth sauce, strain through a fine sieve, if desired.
Season with salt and pepper and keep over a bain-marie. Just before serving, stir in herbs.