Prep the onion. Trim 1/2 inch off the pointy top of the onion but leave the root intact. Peel off the papery skin. Place the onion root-side down. Starting about 1/2 inch from the root, make 8–12 cuts down to the board to create “petals.” Gently turn the onion over and separate the layers so it blooms.

Mix the dry coating. In a bowl, combine 3/4 cup flour, 2 tablespoons cornstarch, 1 teaspoon smoked paprika, 1 teaspoon garlic powder, 1/2 teaspoon onion powder, 1/4–1/2 teaspoon cayenne (optional), 1 teaspoon kosher salt, and 1/2 teaspoon black pepper.

Make the wet mix. In a second bowl, whisk 1 egg with 3/4 cup buttermilk. If you don’t have buttermilk, mix 3/4 cup milk with 1 teaspoon lemon juice and let sit 5 minutes.

First dredge. Dust the onion thoroughly with the seasoned flour, making sure to get between all petals. Tap off excess.

Dip and dredge again. Dip the floured onion into the buttermilk mixture, letting it seep between the petals. Return it to the flour and press the coating on so it clings. This double coating makes it extra crispy.

Preheat the air fryer. Set to 360°F (182°C) for 5 minutes. Preheating helps the coating set quickly.

Oil for browning. Lightly spray the onion all over with cooking oil, or drizzle about 1–2 teaspoons of oil over the petals. Don’t soak it—just enough to help it crisp and color.

Air fry. Place the onion cut-side up in the air fryer basket. Cook at 360°F for 16–20 minutes, until deep golden and crispy. If the tips brown too fast, tent lightly with foil for the last few minutes.

Make the dipping sauce. Stir together 1/2 cup mayonnaise, 2 tablespoons ketchup, 1 teaspoon Dijon mustard, 1–2 teaspoons prepared horseradish (to taste), 1/2 teaspoon smoked paprika, a pinch of garlic powder, 1 teaspoon apple cider vinegar, a few dashes hot sauce, and a pinch of salt. Chill until serving.

Serve. Let the onion cool 2–3 minutes so it sets, then transfer to a plate. Serve with the sauce in the center or on the side. Pull petals apart and dip.