Pour 4 pints of cold water into lg saucepan and bring it to boil. Drop in Kombu, and bring just to boil again, then remove the Kombu and set aside. Stir in the Katsuobushi and turn off heat. Let rest for 2 minutes, then skim off scum. Strain out Katsuobushi. Set both aside. The Stock may be used immediately or can be used up to 8 hours later. Can be kept in fridge for up to 2 days.

From "Recipes-The Cooking of Japan" from Time-Life International, c1965.