I originally found the recipe here, but now I notice it points back to another site with different proportions. I think I'll be using the original next time, and you'll see why!
The sauce is made by whisking apple cider vinegar, ketchup, soy sauce, sugar, and garlic powder. My initial credulity was ketchup. Really? But ketchup originated in Asia. This is one reason why you can find it spelled differently different places, since it was being translated from a different alphabet. So I call possibly legit.
With the sauce ready, I took cut-up chicken and seasoned them then stirred them around with some cornstarch. The original recipe says that they toss it all in a bag. I will be trying that next time.
I also doubled this recipe, and noticed that the original has way more meat the the same amount of sauce. I will be trying that too.
Your coated chicken then gets flash-fried, just enough to get your crispy outside. I also had to do this in batches since they wouldn't all fit in the pan together. After a minute or two, the chicken sits on some paper-towels to get the excess oil off, then right into a baking dish. Next batch!
After all of the chicken has been fried, you pour on the sweet and sour sauce and bake for an hour. Yeah, an hour. Then you look at your mound of dishes. This is certainly the downside of this one.