01 - Slice the peeled onions into very thin rings approximately 1/8 inch thick. Carefully separate all the rings and set aside.
02 - In a large bowl, thoroughly combine the flour, cornstarch, baking powder, garlic powder, paprika, salt, and black pepper until evenly blended.
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 gently until just combined. Avoid overmixing; the batter should be smooth and slightly thick.
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 any excess to drip off before carefully placing them into the hot oil.
07 - Fry for 2-3 minutes per batch, turning once, until golden brown and crispy.
08 - Remove the onion rings with a slotted spoon and drain on paper towels. Repeat with remaining onion rings. Serve immediately with your preferred dipping sauce.