Slice the Chinese cabbage thinly. Cut the tofu into fairly big pieces. Bring the dashi stock to a boil in a small pan, and start by simmering the stalk part of the cabbage first.
When it's cooked add the sake, mentsuyu sauce, soy sauce, tofu, the rest of the Chinese cabbage, and the leek or green onion.
When everything is cooked add the katakuriko dissolved in water and stir in gently. Transfer to a serving plate and top with some grated ginger to taste.