Chop the cabbage.
Salt and soak the cabbage in enough water to cover it. You can skip this step, but the salting and soaking process will create a crispier sauerkraut.
Rinse and drain the cabbage.
Add live sauerkraut or starter culture to the cabbage in a sturdy container. A large stainless steel mixing bowl or pot works well.
Add the 3 tsp salt to the cabbage and pound it with a cabbage crusher. See detailed instructions below.
Pack the crushed cabbage into a fermentation container. Use a cabbage crusher to tamp the cabbage, trying to remove all air bubbles from the container. Be sure to add all of the liquid created when crushing the cabbage.
If you can't cover the cabbage in enough of its own liquid, you can add salt brine to the fermenter. Mix the brine at a ratio of 1 tsp salt per cup of water.
Add fermentation weights to the fermenter to keep the cabbage submerged in the brine.
Ferment at about 70 degrees for 7-10 days. Don't allow the sauerkraut to go above 76 degrees, higher temperatures increases the risk of bad bacteria spoiling the batch. Taste. Ferment longer if desired. Move to a cooler location (basement) and ferment up to 3 months. Be sure to keep the airlock filled with water as necessary.
When you are happy with the fermented flavor, seal the container and store in a cool place or the refrigerator for up to 8 months. You can read about the shelf life of fermented vegetables in more detail in my probiotic fermentation guide.