One or more of:
- dried konbu (kelp) seaweed (konbu)
- clams (asari or shijimi)
- dried bonito flakes (katsuo-bushi)
- dried mackerel flakes (sababushi)
- dried sardines or anchovies (niboshi)
- dried shiittake mushroom mushrooms (hoshi-shiitake)
- dried young "flying fishes" (飛魚;tobiuo or あご;ago,unique name to Japanese-oceanside.)
- If using sardines or anchovies, remove the heads and intestines. Discard these, keeping the bodies.
- Boil fish in water, as if you were making tea.
- Filter the liquid or scoop the solids out of it. The liquid is your dashi.
When only kelp (konbu) is used, you get kombu-dashi. This is bland, and appears to be unpopular for use in miso soup. A chunk of kelp about 6 inches across might be reasonable for a quart of broth.
When sardines or anchovies also used, you get niboshi-dashi. This seems to be the most popular choice for making miso soup. You might add a bit of sake in this case. About 10 little fish (guppy-sized) per quart of broth should do.
When both kelp (konbu) and bonito flakes (katsuo-bushi) are used, you get katsuobushi-dashi. This appears to be the second most popular choice for making miso soup. About 1 cup of bonito flakes per quart of broth should do. At first you produce primary dashi (ichiban-dashi). This is good for clear soups. If you use the solids a second time, you get secondary dashi (niban-dashi). This is good for thick soups and for cooking vegetables.