But when the flavor of dashi is crucial, such as in delicate soups or sauces, it's best to make your own from scratch. Unlike French stocks that are simmered for hours, the key to making good dashi is quick timing. If the kombu is allowed to boil, the stock will be bitter. If the katsuobushi is not strained out within a few minutes, the stock will taste fishy. Using kitchen shears, clip the kombu crosswise in several places to make a fringe.
Place kombu at the bottom of a large saucepan.
Add the cold water and bring to a boil over high heat. Remove kombu just as the water reaches the boiling point. Remove saucepan from the heat and add the katsuobushi flakes. As soon as they settle to the bottom of the pan, strain the stock through a colander lined with a paper coffee filter or several layers of cheesecloth. The wet katsuobushi flakes can be reused in Niban Dashi, or just discarded.