Tau suan is thick mung bean soup sweetened with caramel. It's topped with you char kway (Chinese crullers), which is salty and crispy.
If you know what 豆爽 is, you probably know that "豆" means beans.
What about "爽"? What does "爽" mean?
"Suan" means sticky soup, which may be savory or sweet. I guess "爽" is another word for "羹".
"Cooking for the President" has an alternative explanation that's