Slice onion and dip rings into ¼ cup flour to coat them, shaking off any excess.
To make the batter, combine 1 cup of flour, and the baking powder in a large bowl. Whisk in the milk and egg to make a smooth batter. One by one, dip in the onion rings that have been coated with flour already. Let them drip to remove any excess.
In a shallow bowl, combine the two kinds of bread crumbs, salt, pepper, garlic powder, and cayenne. Stir to mix well.
Dip the battered onion rings into the bread crumb mixture to coat evenly.
Fry the onion rings in a deep fryer with oil at 375 degrees, until golden brown. Drain on paper towel, and sprinkle with additional salt, to taste.