Bring 5 cups of water and 2 dashi packets to a boil in a saucepan over medium heat. Once boiling, reduce to medium-low and simmer for 2-3 minutes. Remove the dashi packets and add sake, soy sauce, and salt. Turn off heat and keep covered.
2
Slice ginger into 8-10 pieces. Slice green onion thinly. Cut the lower half of napa cabbage into quarters lengthwise and tear apart the upper portions by hand. Do not remove the core. Wash and drain well.
3
Place one pork belly slice between each napa cabbage leaf. Use additional pork slices in the outer wider leaves if needed.
4
Remove the core and cut each quarter into 4 pieces. In a large pot, arrange the thicker cabbage leaves along the edges and work toward the center with tender leaves, packing tightly as they will loosen during cooking. Fill the center with loose leaves. Set aside any extra layers to add later if needed.
5
Insert the sliced ginger between the layers.
6
Pour the prepared broth into the pot. Cover and heat over medium-high heat. Once boiling, reduce to medium-low and cook covered for 8-10 minutes until napa cabbage is tender and pork is cooked through.
7
Serve hot in bowls. Garnish with chopped green onion and Japanese seven spice for dipping and seasoning.