Preparation Steps

• Prepare the onion: Cut off the top of the onion, but leave the root intact. Peel the onion. From the root end, cut about 0.5 inch into the onion, stopping before you reach the root itself. Make cuts about 0.75 inch apart, all around the onion, again stopping before the root. Carefully separate the 'petals'.
• Soak the onion petals: Place the onion in a bowl of ice water for about 10-15 minutes to help the petals open up. Drain thoroughly and pat dry with paper towels.
• Prepare the dry ingredients: In a shallow dish, whisk together flour, cornstarch, salt, pepper, paprika, garlic powder, and onion powder.
• Prepare the wet ingredients: In another shallow dish, whisk together eggs and milk.
• Coat the onion: Dredge the onion in the dry ingredient mixture, making sure to get into all the crevices. Then dip it into the egg mixture, letting any excess drip off. Finally, coat it again thoroughly with the dry ingredients, pressing gently to ensure it adheres well.
• Heat the oil: In a large, deep skillet or Dutch oven, heat vegetable oil over medium-high heat to about 350°F (175°C).
• Fry the onion: Carefully place the coated onion into the hot oil, root side down. Fry for about 5-7 minutes, or until golden brown and crispy. You may need to spoon hot oil over the petals to ensure even cooking.
• Drain and serve: Remove the bloomin' onion from the oil and let it drain on paper towels. If any petals are still attached, gently separate them. Serve immediately with the dipping sauce.
• Prepare the dipping sauce: In a small bowl, mix together mayonnaise, ketchup, horseradish, Worcestershire sauce, and paprika. Stir until well combined. Refrigerate until ready to serve.