In a large pot, pour in the dashi stock. Bring to a boil and then add in the sake, mirin, and shoyu. Lower the heat and let it simmer for about 1 minutes. Then add in the napa cabbage leaves and let it simmer until they are soft
In a large pot of boiling water, cook the noodles for about 4 to 6 minutes or as instructed on the package. Drain the noodles and rinse them under cold running water to refresh them and to get rid of extra starch. Set aside
Bring the broth back to a boil. Add in the chicken pieces and the white parts of spring onions, and cook until the chicken is cooked through. Add in the noodles and bring the broth back to a boil. Add in the lightly beaten eggs and partially cover the pot and cook the eggs for about 1 minute (or longer if you want it well done)
Divide the noodles and broccoli into 4 individual serving bowl. Ladle the chicken, egg, napa cabbage and generous amount of soup into the bowl. Sprinkle with chopped green onions and sprinkle with shichimi togarashi
Notes
Refer to how to make Ichiban Dashi / first brew here: http://whattocooktoday.com/ichiban-dashi-stock-the-first-brew.html