NEW YORK (AP) — A copy of what’s being called Stephen Sondheim’s first original cast recording has been found on a misplaced CD, capturing the legendary composer’s budding skills in a student-led musical while at Williams College in 1948. Sondheim was an 18-year-old sophomore when he wrote the music for “Phinney’s Rainbow,” a show that had just four performances sponsored by Williams’ theatrical organization Cap and Bells. Paul Salsini, the author of the new memoir “Sondheim & Me: Revealing a Musical Genius,” recently found the CD while putting away material he had amassed for his book and realized it contained “Sondheim’s first original cast recording.”