Peel the onion, cut it into ½-inch (1–2 cm) slices, and separate the rings.
In a bowl, combine the flour and salt for the flour coating.
In another bowl, whisk together the flour, cornstarch, salt, paprika powder, and cracked pepper. Add in the sparkling water (or beer) and whisk until a smooth batter is formed. You can adjust the consistency by adding more flour if it’s too runny or more sparkling water if it’s too thick. It should be like a slightly thicker pancake batter.
Heat the frying oil in a pot (or small wok) to 350°F/175 °C. You won’t need much oil, but the onion rings should swim in it.
Dip the onion rings first into the flour coating, then into the batter and immediately add them to the oil. Work in batches to prevent overcrowding in the pot.
Let the onion rings cook for 3 to 4 minutes until golden and crispy.
Transfer the onion rings onto paper towels to remove excess oil. Sprinkle them with more salt and enjoy!