01 - Trim onion roots slightly to allow onions to sit flat. Working with one onion at a time, make four evenly spaced vertical cuts from top toward base, without cutting all the way through. Rotate and make four more cuts between previous slices. Carefully separate the onion layers into petals with your fingers while keeping the base intact.
02 - Submerge prepared onions in ice water for 10 minutes to help open the petals fully. Drain well and pat onions dry with paper towels.
03 - In a bowl, combine flour, cornstarch, paprika, garlic powder, onion powder, cayenne pepper, salt, and black pepper. Whisk to blend the dry ingredients evenly.
04 - In a separate mixing bowl, beat eggs with milk until homogenous.
05 - Dredge each dried onion in the seasoned flour mixture, coating thoroughly and shaking off excess. Dip into egg wash, allow excess to drip away, then return to the flour mixture for a second coat. Firmly press petals to secure the batter on all surfaces.
06 - Fill a deep fryer or heavy-bottomed pot with at least 3 inches of vegetable oil. Preheat oil to 350°F (177°C), monitoring the temperature with a thermometer for accuracy.
07 - Fry onions in small batches, cut side down, for 2–3 minutes. Carefully turn and cook another 2–3 minutes, until petals are evenly golden and crisp. Transfer finished onions to a paper towel-lined tray to drain excess oil.
08 - In a bowl, mix mayonnaise, ketchup, horseradish, smoked paprika, garlic powder, a pinch of salt, and black pepper until creamy and blended.
09 - Arrange crispy mini bloomin' onions on a platter and present with dipping sauce for immediate enjoyment.