01 - Peel the onions and slice them into very thin rings approximately 1/8 inch thick. Carefully separate the individual rings and set aside.
02 - In a large bowl, combine the all-purpose flour, cornstarch, baking powder, garlic powder, paprika, salt, and black pepper. Whisk thoroughly to ensure even distribution.
03 - In a separate bowl, whisk together the cold sparkling water and egg until fully incorporated.
04 - Pour the wet mixture into the dry ingredients and whisk until just combined. Avoid overmixing; the batter should be smooth with a slightly thick consistency.
05 - Heat vegetable oil in a deep fryer or large, heavy-bottomed pot to 350°F.
06 - Working in batches, dip the onion rings into the batter, allowing excess to drip off, then carefully place them into the hot oil.
07 - Fry for 2 to 3 minutes per batch, turning once, until golden brown and crisp.
08 - Remove with a slotted spoon and drain on paper towels. Repeat with remaining onion rings. Serve immediately with your choice of dipping sauce such as ranch, chipotle mayo, or ketchup.