Beurre Blanc

Heat vinegar, wine, shallot, peppercorns, and salt in small heavy noncorrosive saucepan over medium heat to boiling. Reduce heat to very low; simmer until no more than 1/2 teaspoon liquid remains when pan is tilted and shallot appears as a moist, mushy purée, about 20 minutes. Immediately remove from heat; cool slightly.

Whisk butter, one piece at a time, into reduction in saucepan; add each piece just as the previous one is almost incorporated. Move pan on and off very low heat as necessary to maintain smooth but not runny consistency; when all butter is added, you should have a thick, creamy emulsion with no greasy streaks. Add drops of lemon juice to taste; strain into warm sauce boat. Serve immediately.