Pour 600 ml water into a pot, add 3 g dried kelp (kombu) and soak for at least 30 minutes.
While you wait, peel and cut your ingredients according to the ingredients list.
After 30 minutes, place the pot on the stove and heat on medium. When the broth starts to gently bubble, remove the kombu and reduce the heat to low. Add 1 tbsp Japanese soy sauce (koikuchi shoyu), 1 tbsp sake and 1 tbsp mirin.
Place the ingredients in the pot starting with harder vegetables at the bottom (1 potato, ½ carrot) followed by 4 leaves Napa cabbage, 2 fresh shiitake mushrooms, ½ onion and ½ Japanese leek (naganegi). Arrange the 200 g firm tofu, 2 salmon fillets and 6 scallops on top.
Increase the heat to medium-high and bring the broth to a boil. Cover the pot with a lid and let it bubble for 5 minutes or until the root vegetables are fork-tender and the salmon is cooked through.
Reduce the heat to the lowest setting and add 3 tbsp yellow miso paste (awase) to a miso strainer. Dip it into the broth and mix thoroughly until dispersed into the soup.
If you don't have a miso strainer, add the miso and a small amount of broth to a bowl and whisk until smooth and loose before pouring it into the pot.
Place 1 tbsp butter on top of the completed hot pot.
Divide into portions and serve with a sprinkle of Japanese sansho pepper.
Once all of the ingredients are consumed, add cooked udon noodles to the leftover broth to finish the dish. Enjoy!
Notes
Note: While the nutritional information includes the full serving of broth, most people in Japan don't actually finish all the soup.