01 - Trim the root end just enough so each onion stands upright without falling apart. Peel off the outer skin. Make 4 to 6 vertical cuts from the top down toward the root, stopping about ¼ inch from the base to keep the layers attached. Rotate the onion and add more cuts to form 8 to 12 petals. Gently pull the petals apart 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 into the flour mixture, ensuring even coverage. Shake off the excess, then submerge in the egg-milk mixture. Transfer back to the flour mixture and press gently so every petal gets a thorough coating.
04 - Pour vegetable oil into a deep pot or fryer and bring to 350°F.
05 - Lower one or two onions into the hot oil cut side down. Fry for 2 to 3 minutes until golden, then flip and continue frying for another 2 to 3 minutes until fully crisp and cooked through.
06 - Lift the onions out with a slotted spoon and set them on paper towels to drain. Sprinkle with additional salt if desired.
07 - Combine mayonnaise, ketchup, prepared horseradish, smoked paprika, garlic powder, lemon juice, and a pinch of salt in a bowl. Stir until fully blended.
08 - Arrange the hot mini bloomin onions on a serving plate alongside the dipping sauce.