Wash and peel onion.
Cut onions into evenly thin slices and ensure they are almost of same thickness.

Sprinkle corn flour on the slices and toss them.
Heat oil in a deep pan till medium hot but not smoking hot.

Reduce the flame to medium. Add few onion slices at one time and deep fry until crisp.
Transfer them to an absorbent paper. Fry all the onions in batches. Cool them completely and store in a airtight jar.