And so I had to go to the store.
*It turns out, sherry vinegar is one of those pricey gourmet things that costs $10 for a tiny bottle and is not carried by major grocery stores. It's the Spanish equivalent of balsamic, although that's sweeter, and the recipe said sub white wine vinegar, so I finished off the tail end of a bottle of balsamic vinegar and used white wine vinegar for the rest. Initial tasting suggests it will work quite well. The More You Know.