Clean the cabbage: Remove any large outer leaves with thick ribs and set them aside. Use a kraut cutter, mandolin, or sharp knife to slice the cabbage. The cabbage can be sliced up to ¼-inch thick or smaller.

In a large bowl, combine the shredded cabbage and kosher salt. Toss the two ingredients together and gently massage the salt into the cabbage. Allow the cabbage and salt to rest until juice begins to collect in the bottom of the bowl, about 4-6 minutes.

Pack the cabbage into a quart jar, slightly pressing to cover it with its own liquid. Pour any remaining liquid in the bowl over the packed cabbage. The cabbage needs to stay below liquid at all times during fermentation. Cut a piece of the reserved cabbage outer leaf into a smaller size that fits into the quart jar. Press the outer leaf onto the shredded cabbage and use it as a weight to keep the cabbage below the liquid.

Put a lid on the jar and place it in a spot out of direct sunlight. Once a day, remove the lid to allow the collected gas to escape. Begin to taste the sauerkraut after 2-3 days. Let the sauerkraut sit for up to 9 days until it achieves the desired sour flavor. Once finished, remove the top piece of cabbage and store the sauerkraut in the refrigerator to stop the fermentation process.