Peel the onions and slice them into 1/2-inch thick rounds. Separate the rounds into individual rings and then cut rings into bite-size chunks (about 1–1.5 inches). Pat the pieces dry with paper towels to remove excess moisture—this helps the batter adhere and reduces splatter when frying.

Make dry mix

In a medium bowl, whisk together the all-purpose flour, cornstarch, baking powder, 1 tsp salt, black pepper, paprika and garlic powder until evenly combined.

Make wet batter

In a separate small bowl, beat the egg lightly then whisk in cold sparkling water. Pour the wet mix into the dry mix and stir just until combined; the batter should be thick enough to coat the onion pieces but still slightly loose. If too thick, add 1 tsp more sparkling water; if too thin, add 1–2 tbs flour.

Prepare coating

Place the panko breadcrumbs in a shallow dish. Toss the onion pieces in the batter to coat thoroughly, allowing excess to drip back into the bowl. Transfer battered pieces into the panko and press gently so breadcrumbs adhere, coating all sides. Place coated pieces on a wire rack or baking sheet while you heat the oil.

Heat oil

Pour vegetable oil into a deep skillet or saucepan to a depth of about 1.5 inches (enough to shallow-deep fry). Heat over medium-high until the oil reaches 350°F (175°C). If you don't have a thermometer, test by dropping a small pinch of batter into the oil — it should sizzle and rise steadily without browning immediately.

Fry in batches

Working in small batches (do not overcrowd), gently lower coated onion bites into the hot oil with a slotted spoon or spider. Fry for 2½–3½ minutes per batch, turning as needed, until golden brown and crisp. Adjust heat to maintain 330–350°F. Remove fried bites with a slotted spoon and drain on a paper towel–lined plate or a wire rack set over a sheet pan to keep crisp.

Season and finish

While still hot, sprinkle the fried onion bites with a light pinch of salt (about 1/4 tsp total distributed over all batches) and toss with chopped parsley if using. Let rest 2 minutes before serving so the interior finishes cooking and the coating sets.

Dipping Sauce (optional)

Combine the mayonnaise, ketchup, hot sauce, lemon juice and 1/8 tsp salt in a small bowl. Whisk until smooth. Taste and adjust seasoning—add more hot sauce for heat or a pinch of sugar if you prefer slightly sweeter. Serve chilled alongside warm onion bites.