A couple months ago, my cousin's wife introduced me to toong mai brought back from a recent trip to HNL. Her family was from Oahu and she grew up eating this snack. She said that Sing Cheong Yuan still has the real deal, cooked in hot sand.
This sweet may be somewhat of an acquired taste. Made with air-dried sweet rice that's barely puffed, this had a very hard, tooth-endangering crunch. Just a little sweet and studded with nuts, it did grow on me. But I didn't let my mother eat any for fear of breaking her dentures.
This article in the Star Bulletin has more info,
Sing Cheong Yuan Bakery
1027 Maunakea St
Honolulu, HI 96817