If your idea of a diva’s master class resembles the Terrence McNally play based on the historic sessions Maria Callas conducted at Juilliard, you’re in for a surprise. Currently appearing at the Met as Virginia Woolf in the premiere stage production of The Hours, by Kevin Puts, Joyce DiDonato mesmerizes not a scintilla less in the studio than she does onstage. Unlike Callas, she plays the role of mentor to the hilt. She comes on dressed to kill. She throws curves, startling the young talent with improv. It’s enthralling theater—yet never an ego trip. DiDonato’s flamboyant methodology takes participants and auditors inside her own never-ending quest for artistic truth. She dives deep and flies high and challenges her charges to do likewise. If you can’t attend live, stream. —M.G.