Place the shredded cabbage in a bowl. Sprinkle the salt on top and start kneading and massaging the cabbage, squeezing firmly to release the juices. I find it helpful to walk away after a couple of minutes and let the cabbage stand and soften further, before kneading further.
Continue doing this for 10 minutes at least. You will see the liquid pool at the bottom of the bowl. Mix in the caraway seeds, if using.
Start packing the cabbage into a very clean or sterilized quart-sized mason jar, pressing down firmly on the shreds after every couple of tablespoonfuls to pack it tightly. Continue packing in the rest of the cabbage this way. Stop when you're about an inch from the top and place the heavy outer cabbage leaf you reserved, folded to fit into the jar, on top of the shredded cabbage.
You should have enough brine now to cover the cabbage shreds and the outer leaf, but if for any reason you don't have enough brine, make extra brine by mixing 1 cup water with 1 ¾th teaspoon salt. Pour it into the jar until all of the cabbage is completely submerged. None of the vegetable should be exposed to the air. This is really important.
Cover the jar with cheesecloth and put a rubber band around the neck to hold it in place, especially if you don't have a two-piece mason jar lid. If you have a two-piece lid, screw it on loosely so the water can vent if needed. Place in a bowl or dish, or on paper towels, in a cool, dark place out of direct sunlight.
Every couple of days check on the sauerkraut. You should start seeing some bubbling in a couple of days, telling you the bacteria is at work. The liquid might overflow when you open it. Make sure there are no shreds of cabbage floating on top, cover and put away again.
I ferment the sauerkraut for seven days and then place it in the refrigerator, but you can let it go as long as two weeks to ferment further and then refrigerate. If at any point the cabbage looks moldy, smells off or looks spoilt, do not taste it. Just throw it away.
Enjoy the sauerkraut in sandwiches, salads, and in just about anything you want some extra flavor and crunch.