01 - Trim the root just enough so each onion stands upright while remaining intact. Peel the outer skin. Make 4 to 6 vertical cuts from the top to the root, stopping about ¼ inch from the bottom so the layers stay connected. Rotate and make additional cuts to form 8 to 12 petals. Gently separate the petals with your fingers.
02 - Combine all dry breading ingredients in a shallow bowl. In a separate bowl, whisk together the eggs and whole milk until smooth.
03 - Dip each onion in the flour mixture, coating thoroughly. Shake off excess, then submerge into the egg-milk mixture. Return to the flour mixture, pressing gently to coat all petals evenly.
04 - Pour vegetable oil into a deep pot or fryer and heat to 350°F.
05 - Fry onions one or two at a time, cut side down, for 2 to 3 minutes until golden. Flip and continue frying for another 2 to 3 minutes until crisp and cooked through.
06 - Remove onions with a slotted spoon and drain on paper towels. Sprinkle with extra salt if desired.
07 - Combine mayonnaise, ketchup, prepared horseradish, smoked paprika, garlic powder, lemon juice, and a pinch of salt in a bowl. Mix until well blended.
08 - Arrange hot mini bloomin onions on a serving plate alongside the dipping sauce.