Clean your mason jar thoroughly by sanitizing or washing it in hot soapy water.

Set aside one piece of cabbage that's slightly larger than the mouth of the jar.

Slice the rest of the cabbage thinly. Aim to make each piece similar-sized, so they all ferment at the same speed.

Place the sliced cabbage in the jar, pressing it down fit as much in as possible. Fill all the way up.

Dissolve sea salt in water to create a brine. Pour over the cabbage, up to about 1cm from the mouth of the jar.

Fit the large piece of cabbage just below the water line, tucking the corners down below the neck of the jar. This will keep the other pieces of cabbage underneath the water's surface.

Place a sheet of paper towel on top of the jar, securing with string/elastic band.

Leave to ferment on a countertop for 4 days, topping up brine if any has evaporated. If white scum appears on top of the cabbage at any point, scoop off with a clean spoon.

After 4 days, sample. If the cabbage is fermented to your taste, screw a lid on the jar and store in the fridge. If not, leave on the countertop for a day or two longer, until desired taste is reached.