What am I doing wrong with my Beurre Blanc?
Julia Child's "classic" recipe for beurre blanc uses quite a lot of butter (3 sticks) to 1/4 cup each of white wine and white wine vinegar (plus shallot and salt and pepper, with a squeeze of lemon to finish).  I suspect that you (a) used too much liquid, and (b) used the wrong vinegar, leading to an overly sour/acetic sauce.