Step 1 Using scissors, make several crosswise slits in the konbu (this helps to extract the flavor during cooking). In a medium saucepan, combine the konbu and water and set aside for 15 minutes. Place the pan over medium heat until the water almost comes to a boil, about 5 minutes. Remove from heat.
Step 2 Cool the mixture for a couple of minutes, then gently add the bonito flakes (do not stir them into the mixture). After 5 minutes (the bonito flakes will have settled to the bottom of the pan), strain the dashi through a very fine mesh sieve, or a sieve lined with cheesecloth. This makes about 3 cups dashi, more than is needed for the remainder of the recipe. The dashi will keep, covered and refrigerated, for 3 to 4 days. Do not stir the dashi as this will cloud it; it should have a light golden color.