Cut the cabbage into quarters length-wise, then slice each quarter into half inch pieces.
Place sliced cabbage into a large bowl. Sprinkle 1/4 cup sea salt and toss evenly into the cabbage.
Let the salted cabbage sit for 3 to 4 hours, or until the cabbage pieces shrink in size and release a good amount of cabbage juice. To speed up the process, massage the cabbage with hands.
Squeeze out as much cabbage juice as possible, and place the cabbage in a seperate bowl. Add the daikon into the same bowl with the cabbage.
Put the rest of the ingredients, including garlic, onion, apple, ginger, fish sauce, and red pepper powder into the food processor.
Blend all the ingredients in the food processor into a paste.
Pour the paste into the bowl of cabbage and daikon. Mix the paste with cabbage and daikon until well combined.
Transfer the kimchi mixture into a mason jar, or any glass jar or fermentation crock. Cover the container loosely to allow air pressure to escape. Let the kimchi ferment in a dark spot for up to 7 days. Gently press down the kimchi with a fork if the kimchi starts to rise up due to gas released during fermentation; take care of the fermentation so that it doesn't overflow. You can taste it along the way to check if the flavour is ready. If you live in a warm place, it may take less time to ferment. Move the kimchi to the fridge once fermentation is complete.
Notes
I save the cabbage juice from above step 4. The cabbage juice is full of vitamins, but keep in mind it is very salty. I reuse it to make soup later on. The cabbage juice store well in the freezer for extended time.