Heat the oil in a deep-fryer to 365 degrees F (185 degrees C).
Dip the onion slices into the flour mixture until they are all
coated; set aside. Whisk the egg and milk into the flour mixture
using a fork.
Dip the floured rings into the batter to coat, then place on a wire
rack to drain until the batter stops dripping. The wire rack may be
placed over a sheet of aluminum foil for easier clean up. Spread the
bread crumbs out on a plate or shallow dish. Place rings one at a
time into the crumbs, and scoop the crumbs up over the ring to coat.
Give it a hard tap as you remove it from the crumbs. The coating
should cling very well. Repeat with remaining rings.
Deep fry the rings a few at a time for 2 to 3 minutes, or until
golden brown. Remove to paper towels to drain. Season with seasoning
salt, and serve.