Let me just say that Ms. Goldstein has my deep appreciation for 29A: Mendelssohn work in E flat major, and others (OCTETS). This particular work has long been one of my all time favorite pieces of classical music. Which, by the way, he wrote when he was just 16 years old. But, as Tom Lehrer once said, "When Mozart was my age, he'd been dead for five years!"
Meanwhile, the fun theme is revealed at 58A: One of a pair at the dinner table ... or a hint to this puzzle's theme (SALTSHAKER). There are three rebus squares where NaCl has been mixed up in a novel way, and fit into a pair of long answers. I'm impressed that five of the six answers split the four-letter string across two words, as in AMERI[CANL]IT and VATI[CANL]IBRARY (shout out to Frannie and Horace for the latter).
By the way, apparently they weren't looking for "suprachiasmatic nucleus" at 17A: Circadian rhythm regulator (INTER[NALC]LOCK). Sometimes being a Neurologist is not very helpful.
There are other anagrammatic formulations of the letter string (21 to be exact), so I imagine there are other sets that might work, but I'm not going to work my way through them. I'm sure Ms. Goldstein chose the best options.
Some nice clues include:
46D: Too, for one (ADVERB) - I love the wit of the clue.
49D: Leaf producer (NISSAN) - Nice hidden capital.
I enjoyed this one quite a bit, finishing in 6:22. Nice start to the turn! And it's another debut. So many recently! I love it.