Final answer:
Andy Bernard stars in the musical 'A Funny Thing Happened on the Way to the Forum' by Stephen Sondheim in Season 7, Episode 3 of 'The Office'.
Step-by-step explanation:
In Season 7, Episode 3 ("Andy's Play") of The Office, the character Andy Bernard stars in a local production of the musical A Funny Thing Happened on the Way to the Forum. This musical is a comedy with music and lyrics by the legendary Stephen Sondheim, and the opening number that Andy sings is called "Overture/Comedy Tonight." The musical itself is known for its whimsical humor, catchy tunes, and clever lyrics, all characteristic of Sondheim's renowned work in musical theatre.