Peel onions completely and trim 1/4 inch off the tops. Place root-side down and make vertical cuts starting 1/2 inch from the root, spacing cuts 1/4 inch apart around the entire onion. Make a second set of cuts between the first cuts to create more petals. Gently spread petals open with your fingers.

In a shallow bowl, combine flour, paprika, garlic powder, salt, black pepper, and optional cayenne. In a second bowl, whisk together eggs and buttermilk. Place breadcrumbs in a third bowl.

Hold each onion by the root and dip into seasoned flour, coating between petals. Shake off excess, then dip into egg mixture, coating thoroughly. Press into breadcrumbs, packing crumbs between petals. Set aside and repeat with remaining onions.

Preheat air fryer to 375°F for 3 minutes. Place breaded onions in basket with space between them. Generously spray tops and sides with cooking spray.

Air fry for 15 to 20 minutes until golden brown and crispy at the edges. Check at 15 minutes and adjust time based on your air fryer model.

Serve immediately with ranch dressing, spicy mayo, or bloomin' sauce.