Debone the chicken thighs, leaving the skin intact.
Add the chicken bones, ginger slices, and whole green onions to a pot filled with 12 cups of chicken stock. Cover. Bring to a boil and simmer for 30 minutes.
While the stock is boiling, heat up cooking oil in a large sauté pan over medium high heat. Add the chicken thighs skin side down.
Cook for 5-6 minutes a side, making sure the skin is crispy and the chicken is cooked all the way through. Place the chicken thighs in a metal bowl and pkace a cover over it.
After boiling for 30 minutes, scoop out all of the bones, green onions, and ginger slices. Skim off any scum from the chicken bones.
Add in the 2 cups of water, onions, garlic, potatoes, fish sauce, and soup soy sauce. Simmer on medium high heat for 10 minutes.
Stir in the 3 portions of Kalguksu noodles. Cook for another 5 minutes.
Chop each of the chicken thighs.
Portion out the noodles and broth into a soup bowl. Place a chopped chicken thigh across the top of the soup. Top with a lot of green onions. Finish with some cracked black pepper.