01 - Preheat the oven to 425°F. Line two baking sheets with parchment paper and set aside.
02 - Peel the onions and slice into 1/2-inch thick rings, carefully separating them.
03 - In a shallow bowl, combine flour, baking powder, smoked paprika, garlic powder, salt, and black pepper.
04 - In a second bowl, whisk together eggs and buttermilk until blended.
05 - Place panko breadcrumbs in a third shallow bowl.
06 - Dredge each onion ring in the flour mixture, dip into the egg mixture, then coat thoroughly with panko breadcrumbs, pressing lightly to adhere.
07 - Place coated onion rings in a single layer on the prepared baking sheets and spray lightly with olive oil spray.
08 - Bake for 18 to 20 minutes, flipping halfway through, until golden and crispy.
09 - While rings bake, whisk mayonnaise, sour cream, buttermilk, chives, dill, parsley, garlic powder, onion powder, salt, black pepper, and lemon juice together until smooth. Chill until serving.
10 - Serve the crispy baked onion rings immediately with the chilled ranch dressing on the side.