"Lisa with an 'S'" (the title a parody of the Liza Minnelli TV special "Liza with a 'Z'") was the seventh episode of season 27 and aired Nov. 22.
The Simpsons Wiki, which tracks the show, described it thus (spoilers ahead): "When Homer loses $5,000 at a poker game with Broadway legend Laney Fontaine, the only way he is able to settle the bet is if he loans Lisa to Laney for a month. Then, Laney turns Lisa into a show biz kid and Marge and Homer fear they made a mistake letting her go. So they head to New York to get her back."
It continues, "At New York City, The Simpsons realize how happy Lisa is for [taking part in] a Broadway show, and they decide to go back to Springfield without her. That's when Laney sees that Lisa could easily overshadow her at the shows and so, they could never share the same stage again. This makes Lisa sad and suddenly, she wants to go back home with her family."
Here is a brief clip showing only part of the poker game. Playbill.com will post others once they become available.
There have been numerous Broadway references in "The Simpsons" over the years, including the classic parody of "Trouble in River City" in the episode "Marge vs. The Monorail," and parody musicals based on A Streetcar Named Desire ("A Streetcar Named Marge") and "The Planet of the Apes" ("A Fish Called Selma").
The character Krusty the Klown sings "Send in the Clowns" from A Little Night Music in the episode "Krusty Gets Kancelled," and composer Stephen Sondheim voiced a character based on himself in the episode "Yokel Chords."