It is a good idea to make dashi stock in bulk, divide it into 1 to 2 cup portions, and refrigerate in sealed containers.
1 liter water
30cm konbu seaweed
20g dried bonito (or sardines)
1. Place the water and konbu seaweed in a pot, and start bringing to the boil over medium heat. As the water heats, the konbu will start to unfold. Remove the konbu just before the water starts to boil, then add the dried bonito.
2. Keep boiling for 2 to 3 more minutes until the dried bonito sinks to the bottom.
3. Drain the dashi through a colander lined with kitchen paper.