Put the water and dashi stock in a saucepan and bring to the boil.
Add the ingredients marked ☆ and the atsuage. Put the lid on and let it simmer for about 3 minutes.
Turn off the heat and add the grated daikon radish.
Turn the heat on again, turn the atsuage over, and let it simmer for 2 minutes. Add the katakuriko slurry in small batches, and allow the sauce to thicken.
Transfer to serving bowls, and top with the chopped scallions to finish.