Step 1 of 4

Warm the broth

Put the dashi, soy sauce and mirin into a saucepan and bring it to a bare simmer over a medium heat. Taste it: it should be clearly savory and only faintly sweet. Keep it hot but do not let it boil hard.

— A hard boil drives off the delicacy that is the whole point of dashi. You are warming it, not cooking it.