Think of how often a dish starts with a sauté of onions, carrots, and celery. In Italy this combination is called soffritto. In France it is cooked with butter and called mirepoix, but for general purposes I like it cooked with a light flavored olive oil or even grapeseed oil, which is neutrally flavored, so I call it by the Italian name. I like to make this in larger batches, removing some when it is still pale, or blond, then cooking the remaining amount until it is a darker shade of amber, giving it a caramelized flavor. I sometimes even let some go until it is quite dark, like tobacco, for a very deep flavor. I then freeze it in batches. I use large zip bags and flatten out the soffritto in the bags, making it easier to stack and easier to simply break off the amount I wish to use. Some people freeze it in ice trays as you might pesto. However you store it, having this in the freezer is like having a time machine. It can make having good tasting food on the table much quicker, or if you have several pans going at once it is quite helpful as well as it is easy to burn smaller amounts of onions.