Crispy ried onions used for Biryani and as a base for gravy are called Beresta. Dum Biryani, especially the Hyderabadi one is generously sprinkled with Beresta. Since fried onions are very flavourful, they impart their fragrance to any dish that they are added to.
3 large onions
Corn flour as required
Peel the onions and wash them. Dry them thoroughly and slice them thinly and uniformly. These slices have to be of the same thickness, to prevent the thin slices from getting burnt. Sprinkle as much corn flour on the slices as required to coat them well. Mix thoroughly. Heat oil in a pan. Reduce heat and deep fry the onions, in small batches till golden brown and crisp. Drain on a paper towel and, store in air tight container. Use as required.