Reserve 1-2 outer leaves of the napa cabbage and refrigerate for later use (wrap in plastic). Cut remaining cabbage and place it in a bowl with the salt and toss. Add enough cool water to cover the cabbage and stir until salt is dissolved. Keep the cabbage submerged with a plate over the bowl and let stand at room temperature 6-8 hours (giving a stir midway through if possible) or overnight.
Drain the cabbage, saving the brine. Rinse cabbage, drain, squeeze out any excess water and place it back in the bowl, adding the daikon radish and scallions.
Place the ginger, garlic, shallot, red pepper flakes, fish sauce (or alternatives) and sugar in your food processor. Process until well combined, pulsing, until it becomes a paste. Scoop over the cabbage and using tongs or gloves, mix and massage the vegetables and the red pepper mixture together really well, until well coated. Pack the cabbage into a large quart glass jar or a crock, 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. Place the whole cabbage leaf over top, pressing down - this should help keep the kimchi submerged under the brine. You can also use a fermentation weight placed over top the whole leaf to keep it submerged.
Cover loosely with a lid (allowing air to escape) and place the jar in a baking dish (or big bowl) to collect any juices that may escape.
Leave on the counter for 3 days, then store in a sealed jar in the refrigerator where it will continue to ferment. You can press down on the kimchi daily with the back of a wooden spoon to keep it submerged.
After 3 days, the kimchi is ready, but won’t achieve its full flavor and complexity, until about 2 weeks (in the fridge) slowly fermenting. The longer you ferment, the more complex and sour the taste.
This will keep for months on end in the fridge (as long as it is submerged in the brine) and will continue to ferment very slowly, getting more and more flavorful.
To serve it in a bowl as a side dish, scoop out using a slotted spoon, drizzle with sesame oil, toasted sesame seeds, and fresh scallions.