Find kombu and katsuobushi (bonito flakes) in Japanese markets, in well-stocked supermarkets, or online. Monitor the dashi's temperature with a thermometer. If desired, you can save the spent kombu and katsuobushi to make niban dashi (second stock) for stews and curries where dashi isn't a standout component.

Combine water and kombu in medium saucepan and let stand for at least 1 hour or up to 8 hours. While kombu is soaking, line large fine-mesh strainer with double layer of cheesecloth, letting excess hang over sides. Set strainer over large bowl or 8-cup liquid measuring cup and set aside.

After kombu has soaked, place saucepan over medium-low heat and cook until kombu-water reaches 150 degrees (water should be steaming, with bubbles forming and clinging to bottom and sides of saucepan but not rising to surface), 7 to 8 minutes. Using tongs or spider skimmer, remove kombu and reserve for niban dashi or other use.

Increase heat to high and cook until water reaches 200 degrees (bubbles should break surface just at edges of saucepan; do not let boil), about 3 minutes. Remove saucepan from heat, add katsuobushi, and let steep for 3 minutes. Drain dashi in prepared strainer. Gather sides of cheesecloth to form bundle and lightly pinch with tongs to release any liquid into bowl. Discard bundle or reserve katsuobushi for niban dashi. Dashi can be used immediately, refrigerated for up to 2 days, or frozen for up to 1 month.

To Make Niban Dashi (Makes 3 cups): Bring 4 cups water, spent kombu and spent katsuobushi from ichiban dashi to simmer in medium saucepan over medium heat. Simmer for 10 minutes. Off heat, stir in ¼ ounce katsuobushi and let steep for 3 minutes. Drain through fine-mesh strainer lined with double thickness cheesecloth set over large bowl or 8-cup liquid measuring cup. Gather sides of cheesecloth to form bundle and lightly pinch with tongs to release any liquid. Discard bundle.

Brew Pitch-Perfect Dashi in Three Simple Steps