Step 1: Prepare the Onion
Peel the onion and trim about 1/2 inch off the top, leaving the root end intact.
Place the onion cut-side down. Starting about 1/2 inch from the root, make downward cuts all around the onion to create 12–16 sections.
Carefully separate the onion layers into “petals” without breaking them apart.
Step 2: Season the Flour Mixture
In a large bowl, whisk together flour, paprika, cayenne, garlic powder, onion powder, salt, and black pepper.
Step 3: Make the Wet Batter
In another bowl, whisk together eggs and milk until smooth.
Step 4: Coat the Onion
Place the onion in the flour mixture and gently coat all the petals.
Dip the onion into the egg mixture, making sure it’s fully covered.
Return the onion to the flour mixture and coat again for extra crispiness.
Step 5: Fry the Onion
Heat vegetable oil in a deep pot to 375°F (190°C). The oil should be deep enough to submerge the onion.
Carefully lower the onion into the oil, cut-side down, using a slotted spoon or tongs.
Fry for 7–9 minutes, until golden brown and crispy.
Remove and drain on paper towels.
Step 6: Make the Dipping Sauce
In a small bowl, combine mayonnaise, ketchup, horseradish, paprika, salt, black pepper, and cayenne pepper.
Mix until smooth and creamy.
Step 7: Serve
Place the hot Bloomin’ Onion on a platter, serve with dipping sauce in the center, and enjoy immediately.