Cut sweet onions into 1/2-inch thick rings, gently separate layers and pat them thoroughly dry with paper towels.

Whisk together all-purpose flour, cornstarch, baking powder, salt, black pepper, and paprika in a bowl until evenly mixed and free of lumps.

Pour cold sparkling water and the beaten egg into the dry mix, stirring gently until a smooth batter forms with no dry streaks remaining.

Warm vegetable oil in a heavy-bottomed pot to 350°F over medium-high heat, ensuring about 2 inches of oil depth.

Dip onion rings into the batter, allowing excess to drip off before transferring into the hot oil.

Gently slide battered rings into oil and fry for 2–3 minutes, turning halfway, until golden brown and crisp.

Transfer fried rings onto a wire rack or paper towels, letting them rest for 1 minute to shed excess oil.

Sprinkle with seasoned salt, arrange on a platter, and serve warm with your favorite dip or aioli.