11/4 ounces konbu
5 cups cold water
2 cups dried bonito fish flakes
Gently wipe the konbu with a damp cloth. Fill a pan with the water, add the konbu and leave it to stand, covered, for 6–8 hours. Remove the lid and, on a low heat, bring the water to a near boil.
Remove the konbu just before the water boils as it will give off a strong smell and bitter flavour if boiled at this point.
Bring the stock to a full boil then immediately add the dried bonito flakes, remove the pan from the heat. Do not stir and allow the flakes to settle to the bottom of the pan for a few minutes, skim any foam from the surface. Pass the dashi through a muslin-lined sieve without pressing it.
The dashi will keep in the fridge for a few days and in the freezer for up to 3 months.