Prepare the onions: Peel the onions and slice them into 1cm-thick rounds. Gently separate the rings, discarding the tiny inner ones or the very small outer ones. You want nice, sturdy rings. You’ll hear a clean, crisp snap as you separate them.

Soak the rings (optional but recommended): Place the separated rings in a bowl of ice-cold water and leave them for 20 minutes. This step tempers the raw, pungent bite of the onion, making them sweeter and more mellow when cooked. Drain them and pat them extremely dry with a clean tea towel. Any moisture here will cause the batter to slide off.

Make the dry mix: In a wide, shallow bowl, whisk together the plain flour, cornflour, baking powder, salt, smoked paprika, garlic powder, and black pepper. The cornflour is our secret weapon for that extra-light, crispy texture.

Make the wet batter: In a separate bowl, whisk the beaten egg into the cold buttermilk until fully combined. The mixture will look smooth and pale.

Heat the oil: Pour the oil into your heavy-based pot, ensuring it’s no more than a third full. Heat it to 180°C (350°F). If you don’t have a thermometer, a cube of bread dropped in will turn golden brown in about 60 seconds. The oil should shimmer and have a gentle, rolling heat.

Set up your dredging station: Take a handful of dry mix and toss a few onion rings in it, shaking off any excess. Then, dip them into the wet batter, letting any extra drip off. Finally, return them to the dry mix for a second coating. Press the flour gently onto the rings. This double-dip creates the characteristic craggy, crunchy crust.

Fry in batches: Carefully lower 4-5 battered rings into the hot oil. Do not overcrowd the pot; the temperature will drop and you’ll end up with greasy rings. You should hear a vigorous, steady sizzle as they hit the oil. Fry for 2-3 minutes, turning once with a slotted spoon, until they are a deep, burnished gold.

Drain and season: Use the slotted spoon to transfer the cooked rings to a wire rack set over a baking tray. Sprinkle them immediately with flaky sea salt while they are still hot. The sizzle will subside, and you’ll see the salt crystals glisten on the hot, crispy surface.

Repeat and serve: Continue with the remaining rings, allowing the oil to come back up to temperature between batches. Serve them straight away, while the crunch is at its absolute peak.