Even though the name is gamjatang (gamja - potato; tang - soup), the main ingredient is pork bone. It's hard to find pork spine bone so I settled with whatever pork bones I could find. As long as they come with meat instead of just bones. It does take long time to boil the bones. Give yourself around 3 hours time to cook. So if you're preparing it for dinner, get it started earlier or else it will end up as supper. :)
For soup base :
2 lbs of pork bones
6 cloves of garlic
1 thumb of ginger
10 whole black pepper
1/2 green onion
2 dried shiitake mushroom
For stew :
1/2 napa cabbage
1 medium size bowl of kimchee
1 lb soy bean sprout
1 medium size yukon gold potato
1-2 serrano chilli
1-2 green onion (green parts only)
3-4 perilla leaves
3 tbs minced garlic
1 tbs hot pepper flake
3 tbs rice wine
3 tbs fish sauce
2 tbs kikkoman soy sauce
1 tbs belachan mix (South East Asia style shrimp paste with chilli)
2 tbs Korean hot bean paste (gochujang)
Put the bones in a big pot and covered it with cold water. Make sure the bones will only take up half of the pot. Just because we are going to add more stuffs to it later so reserve enough room in the pot. Put 1/2 ts coffee powder. This supposedly helps to get rid of the smell of pork bones. Put the pot on the stove under high heat. Bring it to a boil and turn it off. Using a colander, pour the bones and water into the colander. Then rinse the bones under cold water. Make sure to wash off all the scums/blood that may stick to the bones. Pour the bones onto a bowl. Meanwhile wash the pot clean. And then put the bones back in the clean pot.
Put all other ingredients for the soup base into the pot with about 10 cups of water. Turn on the stove at medium to high heat. Bring it to a boil and then turn the heat down to medium low just enough for the soup to simmer.
Make sure you set the alarm to check every 30 minutes. Let the soup simmer for about 2-2.5 hours.
While waiting for the soup to get ready. Prepare the sauce by mixing all the ingredients for sauce.
Also get the greens ready for the stew. Slice the perilla leaves about 1/2 inch wide. Cut the green parts of the green onions about 1.5 inch long. Wash about 1 small bowl of soy bean sprout. Cut 4-5 leaves of napa cabbage about 1 inch wide and 3 inch long.
Peel the potato and cut into 1.5 x 1.5 inch cube. Boil in cold water with a dash of salt until half cooked. Drain the water and set aside.