There are great singers, and then there is Marilyn Horne. The revered mezzo-soprano—who has triumphed in opera houses and recital halls around the globe—continues to honor the vocal arts by mentoring young singers. Ms. Horne’s perceptive insights, warmth, and humor make her annual master class one of the year’s most eagerly anticipated events. See this brilliant artist coach a group of young singers as part of her workshop devoted to the art of song.