Soak the kombu in the listed amount of water for over 30 minutes.
Heat the kombu in the water from Step 1, bring to a boil over high heat, removing the kombu right before it comes to a boil.
Once it boils, add the bonito flakes and immerse them with chopsticks. Turn off heat once it comes to a boil again.
Skim off the scum, wait until the bonito flakes slightly sink, then line a colander or strainer with a paper towel or cotton cloth before lightly straining out the liquid. Do not squeeze out the remaining moisture.
It's ready to go. When using this dashi for seasoned rice dishes ("takikomi gohan"), be sure to allow it to cool first. This is handy if you freeze it or keep a stock in the fridge.
To use the remaining kombu and bonito flakes to make tsukudani, see Recipe ID: 1586133.
Story Behind this Recipe
This is the way to prepare an authentic, all-purpose bonito dash.
Be careful not to boil it, or else the kombu will become sticky. It's a waste if you don't use the kombu. Try making tsukudani with it! It's great as an accompaniment to rice in bento lunchboxes.