4 cups water
2 handful of dried bonito flakes (or 4 small packs of dried bonito flakes)
[CP: I used about 30g of bonito; one medium-sized package, and a bit more than 4c. water]
Boil water and then add dried bonito flakes in a pot. Let it simmer for 2-3 minutes. Strain it. Use it as instructed in recipes.
Japanese Cooking 101