How can I safely and effectively use pressure canning to preserve onions for long-term storage?

To safely and effectively use pressure canning to preserve onions for long-term storage, follow these steps:

1. Peel and chop the onions.
2. Pack the onions into sterilized jars, leaving some headspace.
3. Add boiling water or a vinegar solution to the jars.
4. Secure the lids and process the jars in a pressure canner according to the recommended time and pressure for onions.
5. Allow the jars to cool, check the seals, and store in a cool, dark place for long-term storage.