Sanitize jar(s) and lid(s) in the oven at 180 F for 5 minutes
Reserve the outside peel of the onion and then thinly slice the rest either in a food processor or with a good knife.
Fill your jar with onions (alternatively, you can slice up one onion in the jar if you are mostly using this for brine to activate other cultures like hummus)
Pour pink salt over the top: 1 Tbsp per quart of onions + liquid (so for a 4 quart jar use 4 Tbsp)
Weigh the onions down with a sanitized fermenting weight or the outside peel of the onion.
Pour a bit of extra virgin olive oil or avocado oil around the outside of the weight to create a coat above the liquid, thereby keeping out the bad bacteria and allowing the gasses to escape.
Seal the jar and wait! 4-7 days is expected for it to fully culture. When the bubbles stop, they are done.