Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
Slice off the top of the onion and the root end, leaving the skin intact. Stand the onion up and make cuts from about 0.5 inch from the root end up to, but not through, the top. Make 12-16 evenly spaced cuts.
Gently spread the onion petals apart to create the blooming shape. Place the onion in the freezer for about 10-15 minutes to help it hold its shape.
In a shallow dish, whisk together the flour, paprika, garlic powder, onion powder, cayenne pepper, black pepper, and salt.
In another shallow dish, whisk together the beaten eggs and milk.
In a third shallow dish, place the panko breadcrumbs.
Dip the onion into the flour mixture, ensuring it's coated thoroughly, especially between the petals. Shake off any excess.
Dip the floured onion into the egg mixture, coating all sides.
Finally, coat the onion with panko breadcrumbs, pressing gently to help them adhere. Ensure good coverage.
Place the coated onion on the prepared baking sheet. Bake for 25-30 minutes, or until golden brown and tender.
Serve immediately with your favorite dipping sauces like ranch, bloomin' onion sauce, or ketchup.
Notes
For an extra crispy onion, you can lightly spray the panko coating with cooking spray before baking.