I haven't visited every Chinese restaurant in the St. Louis area, but I've eaten at quite a few.
So far I've only found one that gets "Springfield-style" cashew chicken right.
I just finished off a #17 combo -- "Crispy Cashew Chicken" -- from Quik Wok at 10665 Saint Charles Rock Road in St. Ann, and it finally occurred to me that I should share the joy.
The combo comes in at under $5 (they take cash only, so don't sashay in with your debit card expecting food; also, they're closed on Sunday) and includes a generous portion of cashew chicken (breaded, deep-fried chicken with cashews and green onions in a brown oyster sauce), a helping of fried rice, and two crab rangoon.
I probably did eat at every Chinese restaurant in Springfield (Missouri) circa the 80s and 90s (I lived right behind Leong's Tea House, owned by the dish's inventor, for two years) and I know my cashew chicken. Quik Wok's is the real thing.
The only place I've had better cashew chicken (unless it was homemade by my Aunt Lois) was a hole in the wall place in Springfield, near the corner of Glenstone and Seminole. That place was still open when I visited a few years ago. I think it may have been called Hong Kong II, but I can't remember for sure.
Note: If the comment thread turns into a tip trade, I'd be interested in where I can find a decent medianoche around here.