Wipe off the konbu seaweed with a dish cloth. Put the water in a pot, add the konbu seaweed and let it sit for 30 minutes to 1 hour. Turn on the heat and remove the kombu just before the water boils.
Turn off the heat for a moment. Add the bonito flakes and turn on the heat again. Simmer for 1-2 minutes and turn off the heat. Skim the scum off the surface.
When the bonito flakes sink to the bottom of the pot, pour through a fine-mesh strainer lined with paper towels.
You can make niban dashi (second dashi), by adding more bonito flakes to the konbu and bonito flakes you just used.
Story Behind this Recipe
This is a recipe that was handed down to me by my mother. It's also delicious if you make it with just bonito flakes. You can make tsukudani (rice topping) with the konbu. It's also delicious chopped and stir fried in sesame oil (flavor it with soy sauce, sake, and mirin) After using bonito flakes to make a second pressing of dashi, I make furikake. I dry roast the bonito flakes and then add sake, soy sauce, mirin and sesame seeds.
For Step 2, heat over medium heat and slowly bring to a simmer. For Step 3, set a pot or bowl underneath. If you squeeze the bonito flakes too much, the dashi will turn bitter, so be careful. When you want to make a strong dashi, add extra bonito flakes. If making dashi with bonito flakes only, increase the amount of bonito flakes.