01 - Peel the onions and slice them into very thin rings, approximately 1/8 inch thick. Carefully separate all rings and discard any loose skin or very small center pieces.
02 - In a large mixing bowl, combine the all-purpose flour, cornstarch, baking powder, garlic powder, paprika, salt, and black pepper. Whisk thoroughly to ensure even distribution of all seasonings.
03 - In a separate bowl, whisk together the cold sparkling water and egg until fully incorporated. The sparkling water helps create a lighter, crispier batter.
04 - Pour the wet mixture into the dry ingredients and whisk until just combined. Avoid overmixing; the batter should be smooth and slightly thick with some small lumps remaining.
05 - Heat vegetable oil in a deep fryer or large, heavy-bottomed pot to 350°F. Maintain this temperature throughout cooking for optimal crispiness.
06 - Working in batches to avoid overcrowding, dip the onion rings into the batter, allowing excess to drip off. Carefully place them into the hot oil and fry for 2 to 3 minutes, turning once, until golden brown and crisp.
07 - Remove the onion rings with a slotted spoon and drain on paper towels. Repeat with remaining onion rings. Serve immediately while hot and crispy, with your choice of dipping sauce.