Preparation Bring cold water and kombu just to a boil in a large saucepan over high heat. Remove from heat and remove kombu (saving it for pickled Napa cabbage ). Sprinkle katsuo bushi over liquid; let stand 3 minutes and, if necessary, stir to make katsuo bushi sink. Pour through a cheesecloth-lined sieve or a coffee filter into a bowl. Reserve katsuo bushi for rice with soy-glazed bonito flakes and sesame seeds . Cooks' notes:• If making stock for miso soup it is not necessary to save the kombu or katsuo bushi. • Stock keeps 4 days. Cool, uncovered, before chilling, covered.