Method

• 01
  Position racks in upper and lower thirds of oven; preheat to 450°F. Coat 2 large rimmed baking sheets with cooking spray.
• 02
  Cut off both ends of each onion and peel. Slice into ½-inch-thick slices; separate into rings. (Discard the smallest rings or reserve for another use.) Place the rings in a medium bowl; cover with cold water.
• 03
  Combine flour and baking powder in a shallow dish. Lightly beat eggs in another shallow dish. Combine breadcrumbs and seasoning in a third shallow dish. Working with one ring at the time, remove from the water, letting any excess drip off. Coat in flour, shaking off any excess. Dip in egg and let any excess drip off. Then coat in the breadcrumb mixture, shaking off any excess. Place on the prepared baking sheets. Generously coat the onion rings with cooking spray.
• 04
  Bake for 10 minutes. Turn each onion ring over and return to the oven, switching the positions of the baking sheets. Continue baking until brown and very crispy, 8 to 10 minutes more.
• 05
  Ingredient note: Look for fine dry whole-wheat breadcrumbs in the natural-foods section of large supermarkets or natural-foods stores. To make your own, trim crusts from firm sandwich bread. Tear the bread into pieces and process in a food processor until very fine. Spread on a baking sheet and bake at 250°F until dry, about 10 to 15 minutes. One slice of bread makes about ⅓ cup dry breadcrumbs.
• 06
  Easy cleanup: Recipes that require cooking spray can leave behind a sticky residue that can be hard to clean. To save time and keep your baking sheet looking fresh, line it with a layer of foil before you apply the cooking spray.