01 - Peel onions and slice into ½-inch thick rings. Separate and set aside.
02 - In a large bowl, whisk together flour, cornstarch, baking powder, salt, black pepper, and paprika.
03 - Gradually whisk cold sparkling water into dry ingredients until smooth and thick enough to coat a spoon.
04 - Heat vegetable oil in a deep pot or fryer to 350°F (175°C).
05 - Dip each onion ring into batter, allowing excess to drip off, then coat with panko breadcrumbs.
06 - Fry the coated rings in batches for 2 to 3 minutes, turning once, until golden and crisp.
07 - Remove rings with a slotted spoon and drain on paper towels.
08 - Serve hot with preferred dipping sauce.