Prep the onion: Slice about 1/2 inch off the pointy top of the onion. Leave the root end intact. Peel the papery skin.

Make the cuts: Place the onion root-side down. Starting 1/2 inch from the root, cut downward into quarters. Then cut each quarter into 3–4 sections, creating 12–16 “petals.” Be careful not to cut through the root.

Bloom it: Flip the onion cut-side up. Gently separate the layers with your fingers to “bloom.” Soak in cold water for 10 minutes to help it open more. Pat very dry.

Mix the dry coating: In a bowl, whisk flour, cornstarch, paprika, garlic powder, onion powder, salt, pepper, and cayenne if using.

Mix the wet coating: In another bowl, whisk eggs and buttermilk until smooth.

Dredge, then dip: Dust the onion with the flour mixture, getting into all the petals. Tap off excess. Dip the onion into the egg mixture. Let excess drip off. Return to the flour mixture and coat again, pressing gently so it adheres. Double-coating gives the best crunch.

Preheat and oil: Preheat the air fryer to 360°F (182°C) for 5 minutes. Generously mist the onion with oil spray, getting between petals. Any dry flour will burn, so spray well.

Air fry: Place the onion cut-side up in the basket. Air fry 10 minutes. Carefully open, mist any pale spots with more oil, then continue 8–12 minutes until deep golden and the inner petals are tender.

Make the dip (optional): Stir together mayo, ketchup, horseradish, smoked paprika, lemon juice, salt, and pepper.

Serve: Transfer the blooming onion to a plate. Garnish with chopped parsley if you like. Serve hot with dip.