In a stock pot, place konbu and cold water over medium heat. Just before the water begins to boil (DO NOT BOIL!) pull off heatand let stand 5 minutes.
Remove konbu, and bring back to heat. Again, right before stock begins to boil, remove from heat and add the bonito flakes. When flakes sink to the bottom, strain through cheesecloth or a fine mesh strainer. Dashi can hold in the refrigerator for 2 weeks.