The first step is to whisk buttermilk and egg together in a shallow dish. Now, whisk flour, cornstarch, smoked paprika, salt, pepper, and garlic powder together in a separate shallow dish.
The next is to add breadcrumbs to a third shallow dish. Dredge onion rings in the flour mixture, then in the buttermilk mixture, then breadcrumbs. Set aside for 10 minutes.
Heat 1 of oil in a large cast iron skillet. You need to fry 3-4 onions at a time for 2 minutes. Enjoy your Onion Rings with Tomato Ketchup!