Wash, rinse and set aside the two outer leaves to top your mason jars for later. Cut the rest of the cabbage into large, finger-size pieces. Put into a large bowl with the sea salt. Add filtered water, making sure cabbage is completely submerged in water. Use a plate or weight if needed and soak overnight (or for at least 6 hours).
Drain the cabbage, but save a few cups of the water to use as brine. Put the drained cabbage, carrots, and scallions in a large mixing bowl. Set aside.
To make the kimchi paste, add the remaining ingredients into a blender or food processor except for the leftover brine. Mix until you form a beautiful red paste.
Massage the paste into the cabbage mix until well distributed. (I suggest using rubber gloves or tongs for mixing.)
Pack the cabbage mixture tightly into two large mason jars or a crock pot, leaving 1-2 inches room at the top for juices to release. Add a little of the reserved brine to just cover the vegetables, pressing them down a bit so they are submerged. Place the whole cabbage leaf on top and press down – this should help keep the kimchi submerged in the brine. You can also use a fermentation weight over top of the whole leaf to keep it submerged. A small ziplock bag filled with water also does the job if you don’t have weights.
Cover the jars loosely with a lid (to allow air to escape) and ferment the kimchi for 3-4 days. Place the jar in a baking dish or large bowl to collect any juices that may escape. (The idea though is to keep as much of the flavorful juice in the jar, so don’t overfill.) Leave the jars somewhere dark and cool for three days (55℉ - 65℉ is ideal). Taste daily to see if it's the desired flavour. Once it reaches your desired tang seal the jars and pop into the fridge. It will continue to ferment slowly even in the fridge and will be good for up to six months.