On today's date in 1784, an Italian violinist named Regina Strinasacchi gave the second of two concerts in Vienna, and had the good sense to commission a new work for the occasion from an up-and-coming young Austrian composer named Wolfgang Mozart.

"We have the famous Strinasacchi from Mantua here right now," wrote Wolfgang to his father a few days earlier. "She is a very good violinist, has excellent taste, and a lot of feeling in her playing—I'm composing a Sonata for her at this moment that we'll be performing together on Thursday."

Wolfgang's papa must have been pleased to hear about the cash commission, but probably would have frowned to learn that Strinasacchi received her part barely in time for the performance, and that his son hadn't even bothered to write out his own part down in full—just a sketchy outline. It also comes as a shock for us to learn that Regina and Wolfgang never got together to rehearse prior to the concert, which meant that she was probably sight-reading her part, and he improvising his.

No matter—the new Violin Sonata was received warmly by Viennese audiences, and afterward Wolfgang had a whole month or so to dot all the musical "i's" and cross all the musicals "t's" in his score before it was printed. And, for the record, this Violin Sonata in B-flat Major is arguably one of Mozart's finest.