For 1qt/l, you're going to need...
Ingredients5cwater1 piecekombu kelp1 handfulkatsuobushi
TimeAbout 10 minutes total (2 minutes active)
Add kombu and water to pan, then slowly bring to a boil over low heat
As soon as water comes to a boil, cut the heat and remove the kombu.
Add katsuobushi to pot and bring back to a boil for 30 seconds, then cut the heat again.
Pour through strainer into a heatproof container.
Use immediately, refrigerate for a week, or freeze indefinitely.