01 - Peel onions and trim the root ends just enough to help them stand upright. Slice each onion into quarters vertically, not cutting all the way through. Repeat with four additional cuts between the previous cuts. Gently spread petals with your fingers.
02 - Place cut onions in ice water for 10 minutes to encourage petals to bloom, then drain well and pat dry.
03 - In a mixing bowl, whisk together all-purpose flour, cornstarch, paprika, garlic powder, onion powder, cayenne pepper, salt, and black pepper until evenly combined.
04 - In a separate bowl, beat eggs and whole milk thoroughly until blended.
05 - Dredge each onion in the seasoned flour mixture, shaking off excess. Dip into the egg and milk mixture, then coat again in the flour mixture. Press gently to ensure an even coating on each petal.
06 - Preheat vegetable oil in a deep fryer or heavy-bottomed pot to 350°F (175°F).
07 - Working in batches, fry onions cut-side down for 2 to 3 minutes. Flip and fry an additional 2 to 3 minutes until they are golden brown and crispy. Remove with a slotted spoon and drain on paper towels.
08 - Mix mayonnaise, ketchup, horseradish, smoked paprika, garlic powder, salt, and pepper in a small bowl until smooth and creamy.
09 - Arrange the fried mini bloomin’ onions on a platter and serve warm with the prepared dipping sauce.