Cut napa cabbage in quarter, and remove stem. In a large bowl, add yellow small part of cabbage leaves as whole, and rest of bigger leaves cut into about 3 inch long and 1 inch wide then add into bowl as well. Doesn’t need to be exact sizes, actually uneven cut cabbage pieces are better for texture.
Mix cold water and sea salt until salt has absorbed; pour over cabbage. Toss cabbage pieces to mix well with salted water and press it down as much as possible. Let it soak for 40 minutes. Half way though time, toss upside down so cabbage will soak evenly.
Meanwhile, let make kimchi paste. Finely chop garlic and cut green onion into half in lengthwise then cut into 1inch long pieces.
Add all ingredients for kimchi paste accept sesame seeds in a mixing bowl and combine, set aside.
Drain salted cabbage and rinse under running cold water for about 1 minute to get rid of excess salt and some dust. Drain completely about 5 minutes.
Combine cabbage and paste in a large mixing bowl and mix with your hand (I recommend you to wear a plastic glove) with gentle pressure and squeeze action, so cabbage will absorb color and flavor of paste very well.
Add toasted sesame seeds and give a light final toss, transfer to a serving plate and serve immediately with some garnish of extra sprinkle sesame seeds.