Remove outer leaves from your cabbage. Save a couple of good leave if you don't have weights to hold your sauerkraut down under the brine
Chop up your cabbage into small pieces or thin strips either by hand or using a thermomix or food processor
Weigh your chopped cabbage
Add 1 tablespoon of Celtic sea salt per kilo of cabbage to your chopped cabbage
Mix the salt through the cabbage and then squeeze and massage the salt into the cabbage by hand until the juices start to be released from the cabbage and pool in the bottom of the bowl.
Once enough juice has come out of the cabbage, pack the cabbage mixture into a fermenting crock or jars. If there is not enough juice to cover, make up a salt brine using 1 tsp salt to 1 cup of water. Dissolve and add to your sauerkraut ensuring all cabbage is under the liquid.
Pack the cabbage down hard so the the juice covers the chopped cabbage, then if using a crock, place weights on top to hold the cabbage under the juice. If using jars, push the saved outer cabbage leaves down into the jar, tucking under the rim, to help hold the chopped cabbage under the juice.
If using jars, place lids loosely on the jars and then place jars or crock onto a dish to catch any overflow (warning - overflow WILL happen as your sauerkraut ferments if your jars are pretty full) and leave your sauerkraut to ferment.
Check your sauerkraut daily (particularly if in jars without weights) as you need to check that your cabbage is under the liquid. If cabbage has floated up to the surface, push it down with a spoon or fork.
Taste your sauerkraut regularly and pop it into the fridge once it develops a sour taste that you like. This may be days or weeks just depending taste. As long as your cabbage remains under the liquid it won't mold.