Wipe the white part of kombu seaweed with damp dish cloth or paper towel.
Soak the konbu seaweed and water in a pan for 30 minutes.
After 30 minutes, heat it over medium and remove the konbu just before it comes to a boil.
Soon after the konbu is taken out, put in the bonito flakes. After it comes to a boil (it should come to a boil right after), turn the heat off and leave for 3 minutes.
Afterward, strain the broth with a strainer and it's done.
(If you want make it saltier, add a pinch of salt).
Story Behind this Recipe
I used to use powered dashi broth. But my mother-in-law made this for hot pot and other dishes, so I asked her how to make it.
You must take the konbu seaweed before it comes to a boil. Otherwise it'll become sticky and the umami of konbu seaweed will be lost. Be careful that it doesn't come to a boil too much after you put the bonito flakes.