1. Slice off the tip of each onion and gently peel and remove the outer skin. Turn an onion root-side down and make 4 vertical cuts with a paring knife at 12 o’clock, 3 o’clock, 6 o’clock and 9 o’clock, leaving the base intact to create petals. Repeat this process for each onion.
2. Add about 3 inches of oil to a large heavy-bottomed pot. Heat the oil to 350ºF over medium heat.
3. Whisk together the flour, garlic powder, oregano, smoked paprika, seasoning salt and cayenne in a large bowl or shallow dish. Combine the buttermilk and egg in another large bowl.
4. Place the onions in the flour mixture with a spoon, tossing slightly until they are well coated; shake off any excess. Submerge the onions cut-side up in the buttermilk mixture. Drain the onions slightly, then dredge them back in the flour mixture, making sure to coat each petal.
5. Carefully place each onion root-side down into the hot oil with a slotted spoon and fry, flipping once, until golden brown, about 2 minutes. Drain on a paper towel-lined plate or cooling rack. Repeat with the remaining onions. Sprinkle with salt and serve warm with the dipping sauce.
1. Mix the mayonnaise, sour cream, ketchup, horseradish, cayenne, pepper and salt in a small bowl.
Tips and Substitutions
Special equipment: a deep-frying thermometer