I saw this is America's Test Kitchen today and they looked so delicious! They used Regular Lay's potato chips and saltine crackers for their breading, but they didn't say how much, I am guessing at least 1/2 cup of each.
Heat oven to 450°F When hot, oil two baking sheet with the oil and place into the oven to get hot, about 8 minutes.
Cut off the ends of the onions and peel the outer layer off. Slice into 2 Inch thick slices. Remove the inside layers to created the rings.
In a food processor, combine the potato chips and the saltine crackers and mix fine into crumbs. Lay them into a medium sized bowl.
In another separate bowl, combine the buttermilk, egg, and salt, pepper, and cayenne and stir to combined.
In a small bowl add the 1/4 cup of flour.
Now to assemble the onion rings. Dip each ring into the flour first to get it dried. Dip them into the buttermilk mixture and then into the crumb mixture.
Lay them onto a dish.
Remove the baking sheets from the oven and place the rings on the hot pans, allowing enough room to fry. There should be 12 rings on each sheet.
Place back in the oven and cook for about 8 minutes. Remove them from the oven and turn each ring to assure both sides get fried. Place back in the oven and continue cooking for about 8-10 minutes and golden brown.