I have done them, thousands of pounds of them way way back in the 1980’s.
I have 2 different methods depending on the moisture content of the onions, if you have well aged onions that have been in storage, a mixture of 1/2 gallon of buttermilk with 7 egss mixed in works very well, dip them, shake off the wet mix, dredge in flour, sake well to remove excess flour, fry without agitating them until browning, try to flip the whole mass over gently to get the upp edges browned without knocking off the breading.
Or, slice your onions, soak the sliced onions in lightly salted water overnight, this is for when you have extra juicy onions that refuse to crisp, and the steam blows your breading off while frying.
Same dredging & cooking techniques.
PS, they destroy your fryer shortening quickly, strain/filter your oil daily to remove the burnt flour. An auto-filtering fryer would be better
