Start by soaking the pork neck in cold water for about an hour to reduce the gaminess. Peel and halve the potatoes, slice the green onions, and prepare any additional vegetables.
In a large pot, fill it up with water and add the pork neck pieces. Bring it to a boil and let it simmer for a few minutes. Drain the water and rinse the pork under cold water to remove any impurities.
Return the cleaned pork spine to the pot and fill it with fresh water. Add soybean paste and ginger. Bring it to a boil and then reduce the heat to a gentle simmer. Cover the pot and let it simmer for a couple of hours (approx 2hrs), allowing the flavours to meld together.
While it's boiling, prepare the seasoning paste. Combine the Gochugaru, Gochujang, minced garlic, soy sauce, fish sauce and perilla seeds.
Parboil the nappa cabbage for a short period, then transfer it into cold water. Gently separate the leaves into long shreds.
After 2 hrs, when the pork is tender, add the potatoes, onion, perilla leaves and green onions. Season with salt, pepper, and any additional seasonings you prefer. Continue simmering until the potatoes are soft and fully cooked.
Optionally, if you have perilla seeds, toss them in for that unique fragrance. At this time, toss in some bean sprouts as well. Adjust the seasoning as needed to achieve that perfect balance of flavours.
Ladle the steaming hot Gamjatang into bowls and garnish with freshly chopped green onions and sesame seeds. Serve it piping hot with a bowl of rice and your choice of banchan (side dishes).