Step #1 Reduce the vinegar, shallots, wine, salt & pepper in a saucepan over med-heat/flame to 1/4 c mixture of solids & liquids.
Step #2 Cool the mixture to 140°F
Place the saucepan with the reduced shallot/wine mixture over extremely low heat & whisk in the butter tbsp by tbsp, whisking vigorously the entire time.
Step #3 Strain the sauce into a sauceboat & serve as soon as possible.