How to Make It
Combine white wine, white wine vinegar, minced shallots, and black peppercorns in a small saucepan; bring to a boil. Cook until reduced to 2 tablespoons (about 4 1/2 minutes). Reduce heat to low. Add chilled butter, 2 pieces at a time, stirring with a whisk after each addition until butter is fully incorporated. Strain mixture through a fine sieve over a bowl; discard solids. Add salt and pepper.