Dissolve the Kuzu starch in water.
Tilting the frying pan with one hand (as the amount of liquid is small), add the Dashi broth, liquid from rehydrating the dried Shiitake, sugar, mirin, and soy sauce. Cook on low heat and mix well with a spoon.
Add 2. to 1. and mix well. Once the sauce thickens and the white cloudiness of the Kuzu starch is gone, it is ready.