With a résumé that includes West Side Story, Gypsy, Sweeney Todd, Into The Woods, Company, and many others, lyricist-composer Stephen Sondheim probably has more to say about musical theater than any human being currently living. He shared some of that knowledge when he took to the stage of London’s National Theatre for an informal and revealing 42-minute interview and Q&A session with director Rufus Norris. Despite his decades of success and innumerable accolades, the sweater-clad Sondheim remains charmingly humble and unpretentious about what he does. Topics include the composer’s troubled childhood with an abusive mother (“My father left her. I can’t blame him.”), his apprenticeship under Oscar Hammerstein II, and his experiences writing for stars like Ethel Merman and Angela Lansbury. He also says that, if he weren’t writing musicals, “maybe I’d be a geologist” and that, when he’s at home, he likes to listen to “concert music that I’ve never heard before.” He admits that “unfamiliar music” is a great source of ideas to steal for one’s own projects.