Use to make Potato-Wrapped Halibut.
Place wine, vinegar, shallots, and sugar in a small saucepan over medium heat. Bring to a boil and immediately reduce to a simmer; cook until liquid is reduced to 2 to 3 tablespoons, 15 to 20 minutes.
Reduce heat to low and slowly whisk in butter, a few pieces at a time, until fully incorporated. Season with salt and serve warm.