This isn't really what tang gook looks like - it doesn't have green onion and the broth is much more brown but it was the closest picture I could find (it's moo gook). For a picture of tang gook, look at the chusuk set up above. This is the traditional soup served on chusuk.
1 moo (daikon)
1/2 pound beef (I use galbi sal)
6 cups water
2 tsp sesame oil
2 tsp gook gan jang (soup soy sauce) and more to taste
1 tsp pepper
salt to taste
Slice the moo. Cut beef into bite size pieces. Saute the beef in sesame oil and soy sauce until browned. Add 6 cups water, moo, sliced onion, and pepper. You can also add thin slices of tofu if you want. Bring to boil. Add gook ganjang and salt to taste. Simmer for 15-20 minutes. You can easily increase the ingredients in this soup for larger portions.