Put the chopped onions in a 1-litre glass pot.

Add ½ cup apple cider vinegar and 1 tablespoon Himalayan salt.

Fill up with filtered water so that it covers the onions, leaving at least 2cm space between the water and the lid.

Put on the lid and let it stand on the counter for 6-8 hours. After this time, put it in the refrigerator.

Allow to stand for 24-28 hours before eating. It keeps in the fridge for weeks and gets sweeter and sweeter!