Dashi is a quick all-purpose quick clear stock that is the heart of Japanese-style cooking. Made properly it is described as tasting of the sea. It calls for (also called kombu), which is a thick dried kelp that is an essential ingredient in Japanese broths, and bonito flakes, pale pink shavings made from dried bonito fish fillets. Look for the seaweed and bonito flakes in an Asian grocery or the Asian food section of a well-stocked supermarket. Dashi is so quick to make that you can make it fresh each time you need it. Beth likes her version with one dried shiitake mushroom added.
Place the water in a medium saucepan. Add the kombu. Bring to a low boil over medium-high heat. Reduce the heat to low (if the water continues to boil, the stock will not be totally clear) and simmer for 5 minutes. Add the bonito flakes and stir. Turn off the heat and let stand for 2 minutes to allow the bonito flakes to settle. Skim off any foam.
Line a large colander or strainer with cheesecloth and set it over a large bowl; carefully pour the dashi through to strain it. Discard the kombu and bonito flakes. The stock is ready for use and can be refrigerated for up to 3 days, but is best used the day it is made.