To order from the walk-up window at Scooter's Frozen Custard, just pull the string next to the window. It is connected to a bell inside, which clanks back and forth a few times, alerting the staff inside that you're ready. This is an operation built almost entirely on frozen custard, and it's a silky smooth foundation.
'frozen custard' on Serious Eats
Chicago is a great food city, one of my top three in the world, but it's a lousy ice cream and frozen custard 'burg. Until fairly recently you had to go to neighboring Wisconsin for standout frozen custard. But everything I tried at Scooter's, a six-year-old, seasonally open mom-and-pop frozen custard shop, was killer.