Frying in a deep fryer, deep-pan or pot will yield the crispiest, most flavorful onion rings. It is the preferred method.
If using a deep fryer, heat frying oil (I like peanut or vegetable) to 325-350 degrees F (160-180 degrees C). Place onion rings in batches for 2-3 minutes each, until browned and crisp
If using an oven: Place the coated rings on a lined baking sheet and spray them generously with a cooking oil spray like coconut oil. Bake them at 425 degrees F (220 degrees C) for 20-25 minutes, flipping at 15 minutes.
If using an air fryer, spray the air fryer basket with oil or cooking spray, place the onion rings in a single layer, and spray them generously with the cooking spray. Cook on 375 degrees F (190 degrees C) for 10 minutes. Flipping halfway through.