What Japanese stock is commonly made from kombu and katsuobushi? Dashi is the answer. It is a family of Japanese stocks, most famously made by steeping or heating kombu, an edible kelp, with shaved katsuobushi, dried and fermented skipjack tuna.
The ingredients contribute different forms of umami. Kombu is rich in glutamic acid, while katsuobushi supplies inosinic acid; together, these compounds produce a stronger savory effect than either ingredient alone. The liquid is usually strained before use.
Dashi is a foundation for miso soup, clear soups, noodle broths, simmering liquids, okonomiyaki, and takoyaki. It is not one fixed recipe: kombu-only, dried-sardine, and dried-shiitake versions are also common, including vegetarian and vegan styles.
A common mix-up is treating dashi as synonymous with fish stock. Some dashi contains fish, but “dashi” refers more broadly to Japanese stock. Kombu should generally not be boiled hard, because it can release bitter or slimy flavors.