Heat oven to 200C/180C fan/gas 6.
Put the flour in a large sealable plastic
bag. Season, then tip in the onion and
shake well. Whisk the egg whites until
foamy, add the onions and stir to coat.
Lightly oil a baking sheet. Add the
seasoning and breadcrumbs to the bag;
then, working in batches, add the eggy
onion rings and coat in the crumbs.
Arrange onion rings, in a single layer, on
the baking sheet and cook for 25-30 mins,
turning halfway through, until the onion is
tender and the crumbs are golden.