Cup of Yum
1. Gather all the ingredients. Please note that this homemade shiro dashi is NOT as concentrated as store-bought shiro dashi; therefore, you may need to make more.
2. In a saucepan, combine 2 cups water and 1 piece kombu (dried kelp). I tore the kombu in half to fit in the saucepan. If you have time, you can do this step in advance (up to overnight) and make cold brew Kombu Dashi.
3. Bring the liquid (or cold brew kombu dashi) to a gentle simmer on medium-low heat. Right before simmering, remove the kombu from the saucepan. If you leave the kombu in the saucepan, the dashi will become slimy and bitter. 
4. Add 2 Tbsp usukuchi (light-colored) soy sauce, ⅓ cup mirin, and 1 Tbsp Diamond Crystal kosher salt. Mix it all together and bring it back to a simmer.
5. Once simmering, add ⅔ oz katsuobushi (dried bonito flakes). For thick shaving katsuobushi (atsukezuri), let it simmer on low heat for 10 minutes. For thin shaving katsuobushi (hanakatsuo), simmer on low heat for 30 seconds, turn off the heat, and let steep for 10 minutes.
6. Finally, strain the shiro dashi into a fine-mesh sieve over a mason jar. You can use the spent thick shaving katsuobushi to make Katsuo Dashi (it will be niban dashi or the second, less flavorful dashi). Use the spent thin shaving katsuobushi to make Furikake (Japanese rice seasonings). Use the spent kombu to make Simmered Kombu.

To Store

Cup of Yum
1. Let the Homemade Shiro Dashi cool completely. Close the lid and store in the refrigerator for up to 3–4 days.

To Use the Shiro Dashi

1. You can use Shiro Dashi to make Udon Noodle Soup, Chawanmushi, Tamagoyaki (Japanese Rolled Omelette), Takikomi Gohan, Oden (Fish Cake Stew), Eggplant Agebitashi, Zosui (Japanese Rice Soup), Kanto-Style Ozoni, and all kinds of simmered dishes (nimono).