How to Make It
Cook wine, vinegar, shallot, and 2 tablespoons water in a large skillet over medium-high, stirring occasionally, until liquid reduces to 2 to 3 tablespoons, about 12 minutes.
Reduce heat to low. Gradually whisk in butter, a few tablespoons at a time, until sauce coats the back of a spoon. Remove from heat, stir in salt, and serve.