1. Fill a medium saucepan with 8 1/2 cups water. Add kombu and place saucepan over medium heat; slowly bring to a boil. Just before water begins to boil, remove kombu using a slotted spoon and discard.

2. When water comes to a full boil, add 1/3 cup more water to saucepan; add bonito flakes. When the water returns to a boil, immediately remove saucepan from heat. Let bonito flakes sink to the bottom of the saucepan; skim off any foam that rises to the top and discard.

3. Strain mixture through a fine mesh sieve, discarding solids. Set liquid aside until ready to use.