Sauerkraut.

Slice the cabbage finely and add 1-2.5% of its weight in salt. The salt creates an environment that allows the good microorganisms present on the surface of the cabbage to outcompete the bad microorganisms producing rot and mold.

Massage the salt into the cabbage. You can add spices at this point, caraway seeds, bay leaves and juniper berries are traditional choices but use what you feel like. You can also add a little grated carrot or apple for flavour.

Pack the cabbage very tightly in clean flip top jars. The salt should draw enough water out of the cabbage to cover the cabbage entirely in brine. Some people adds a dash of white wine to their sauerkraut, thereby creating Weinkraut. Place a small plastic bag full of 2% brine on top of the cabbage to make sure it is all submerged in the brine. It is important to prevent the cabbage from being exposed to the air as it will otherwise rot.

Now leave the cabbage to ferment at room temperature. You should see bubbles of co2 forming in the cabbage after a few days. It's supposed to do this. Taste the cabbage after a week or so. If you're happy with the acidity move your sauerkraut to the fridge which will slow the fermentation down to almost a standstill. Leave the sauerkraut at room temperature for a few more days if you want it more acidic. The cabbage will continue to ferment, until all the sugars in the cabbage has been fermented into lactic acid.

Sauerkraut will keep for months if you make sure to practice good hygiene handling it. You can eat it raw in salads or as topping on sandwiches or you can add it to soups and stews.