When you're doing a show about Maria Callas giving a master class, it helps if there's a genuine diva around to play the role, and for this Miners Alley Playhouse production of Master Class, director Robert Kramer scored a coup when he cast local mezzo-soprano Marcia Ragonetti — even though she didn't get to sing very much. But watching Ragonetti explain technique for the very talented performers who did sing, you understood that she knew exactly what she was talking about. And when she demonstrated at one point just how to make an entrance, it was mesmerizing — and pure diva. RuPaul, eat your heart out.