01 - Peel the onions and slice them into very thin rings, approximately 1/8 inch thick. Carefully separate the individual rings and discard any very small or broken 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 beaten egg until fully combined. The water should remain very cold for optimal batter texture.
04 - Pour the wet mixture into the dry ingredients and whisk until just combined. Do not overmix. The batter should be smooth and slightly thick, coating the back of a spoon.
05 - Pour vegetable oil into a deep fryer or large, heavy-bottomed pot to a depth of at least 3 inches. Heat to 350°F. Maintain this temperature throughout frying for consistent results.
06 - Working in batches, dip the onion rings into the batter, ensuring complete coating. Allow excess batter to drip off briefly before frying.
07 - Carefully place the battered rings into the hot oil. Fry for 2-3 minutes per batch, turning once midway through cooking, until golden brown and crispy. Do not overcrowd the pot.
08 - Remove the fried rings using a slotted spoon and transfer to paper towels to drain excess oil. Serve immediately while hot and crispy, with your preferred dipping sauce.