Step 1: Clean your equipment thoroughly. Remove the outer leaves of the cabbage, rinse them, and set one large leaf aside for later use.
Step 2: Core the cabbage and slice it into very thin ribbons using a sharp knife or a mandoline slicer.
Step 3: Place the shredded cabbage in a large bowl and sprinkle with the sea salt. Let it sit for 10 minutes to allow the salt to start drawing out the moisture.
Step 4: Using clean hands, massage the cabbage vigorously for 10-15 minutes. You are finished when the cabbage has reduced in volume significantly and there is a pool of brine at the bottom of the bowl.
Step 5: Pack the cabbage into a clean glass jar, pressing down firmly with your fist or a tamper to remove air pockets. Ensure the brine rises above the cabbage.
Step 6: Place the reserved cabbage leaf on top of the shredded cabbage and add a fermentation weight to keep everything submerged. Close the lid loosely or use a fermentation airlock.
Step 7: Store the jar at room temperature out of direct sunlight for 7 to 14 days. Taste it daily after the first week. Once it reaches your desired tanginess, move it to the refrigerator.