It can take a lot of time to chop and prepare onions. To speed up future recipes, to reduce waste and spoilage, or to take advantage of low prices, try preparing onions in advance and freezing them for later use. As with most vegetables or fruits, onions can be kept for in the freezer for several months if you prepare them properly. Unlike many other vegetables, onions don't need to be blanched before freezing.
Rinse the onions. Remove the flaky skins and throw them away.
Chop or dice the onions, either by hand or in a food processor or chopper.
Press out as much moisture as possible with a paper towel.
Place onions in a freezer bag or an airtight container. Press out excess air if you use bags, then seal them. Use a permanent marker to label the container with the date.
Place the bag or container in the freezer.
Freeze the onions in small batches so they freeze quickly and are a useful quantity for single recipes. For most cooked dishes, you can add frozen onions to the dish without thawing. Some onions become soft after freezing. These types work best in soups and stews where they don't need to be crunchy.