Actually, it never existed. Not in real life.
And happily, Twitter just led me to this late-April Daily Campus writeup — a rundown of classic summer meals and desserts, with many a local shout-out. Milkshakes from Highland Park Soda Fountain, which recently had its 100th anniversary (and is noted here as Highland Park Soda Shop), made the top of the list.
Have a look. It’ll get you peckish.