You can buy pre-fried onions at almost any Indian grocery store (Sultan and Hanif brands are good products) or fry your own ahead of time. You may also fry the onions just before beginning a recipe, but having them ready makes cooking so easy. To prepare, cut onions in medium dice and sauté in oil. Unless otherwise noted in the recipe, cook to a medium golden color, stirring often to brown evenly and avoid burning. Drain the oil and continue with the recipe or store the onions in a jar in the fridge for future use.