Combine the onions and cornflour in a bowl, tossing to ensure the onions are evenly coated.

Heat a 3cm depth of oil in a large saucepan or frying pan over a medium heat until it reaches 160C, or a piece of onion sizzles when you drop it in. Fry the onions in batches for 5-8 mins, stirring regularly until golden and crispy. Remove to a plate lined with kitchen paper using a slotted spoon to drain. Season generously with salt. Will keep in an airtight container for up to four days.