I forgot where I got this recipe. I think it was on You Tube somewhere. I have tried this and these are the crispiest damn onion rings I have ever had.
½ C flour
¼ C cornstarch
2 T instant mashed potatoes
1 C cold club soda
2-3 yellow onions ¼ slices; no thicker
2-3 C panko bread crumbs
350 degree oil for 2 ½ – 3 minutes
These will stay crispy for twenty minutes after they are done frying.