Wipe the kelp with a wet paper towel. Put the kombu kelp and the bonito flakes in water.
Bring the water to a boil slowly on low or medium heat. NEVER USE HIGH HEAT. Simmer the mixture for 2-3 minutes. (The whole process should take about 12-15minutes)
Strain the dashi through a sieve over a bowl.
If you are not using the dashi right away, save it in a bottle and keep in the refrigerator for 3-5 days, but remember that fresh dashi is the best.
Recipe Notes
The most important thing is that bring the water to a boil very slowly on low to medium heat instead of using high heat. Never use high heat.