Let the cabbage leaves wilt outside in the sunlight for 1 hour.
Wash your hands thoroughly with soap.
After drying, wash the wilted cabbage leaves and pat dry. Chop them in half and shred them with a knife so that they are approximately 0.8 of cm. (See pictures above for examples)
With the Vietnamese mint, pull the leaves off the stem and roughly chop. Cut the onion into small wedges and pull each layer apart.
In a bowl, combine the sugar and salt with the the cooled boiled water.
In a bowl, toss the cabbage, onion and Vietnamese mint
Before pickling, pour boiling water into your 2 - 3 clean medium sized jars and swirl the water around. Discard the water and repeat.
Put cabbage mixture into the jars and squash them in. Pour the pickling liquid over the top until covered.
Make a plastic cut out or fill a zip lock bag with some water and put it on top of the cabbage to keep it completely submerged in the pickling liquid. (see picture above) (Note 1)
Place the lid on and leave it at room temperature for 2 - 3 days.
Refrigerate after opening.
Notes
To make a plastic cut out, I use the packaging of a blueberry or strawberry box. I simply cut a corner off like in the progress picture above and then cut a slit into the center. Then bend the cut out into a cone by pushing the two cut edges past each other and place on top of the cabbage. If you have a small zip lock bag, put a bit of water in it and place it on top of the cabbage. You may have to adjust a few times so that you are able to screw the lid on.