Place buttermilk in one bowl and set aside. Mix flour, salt, pepper, and baking powder in separate bowl. Heat oil at 375 for frying.
Dredge onion rings in flour mixture first, then dip in butter milk and then coat with flour mixture again. Place onion rings in hot oil and do not crowd onion rings. When onion rings are golden brown remove from oil and drain. More salt may be added to your taste.