I've calculated the amounts to use up a 100 g pack of bonito flakes in 3 batches. This recipe will teach you how to make ichiban/first dashi, niban/second dashi, how to use up the konbu seaweed used in dashi, how to store dashi, etc.
Soak the konbu seaweed in water (for the ichiban/first dashi) overnight.
Heat water and konbu seaweed from Step 1. When it comes to a boil, remove the konbu seaweed. Add extra water plus all the bonito flakes at once and bring to a boil. Turn off the heat as soon as it boils.
When the bonito flakes sink to the bottom (in 2-3 minutes) either scoop out or strain the dashi through paper towels.
Put the used konbu seaweed and bonito flakes in water for niban/second dashi and bring to a boil. Simmer over low heat for 5 minutes. If adding adding more bonito flakes for flavor, add 1/2 the amount used for the ichiban dashi.
Store dashi you'll use right away in a pot (it'll keep for 2-3 days). To store dashi longer (up to 3 weeks) pour into ice trays, or into a plastic ziplock bag and freeze flat.
Use ichiban-dashi for clear soups and miso soups, and other dishes that call for it. Use niban-dashi for simmered dishes and the like.
I recommend simmering niban-dashi and konbu seaweed used for making dashi with vegetables in a pressure cooker. The dashi flavor penetrates the vegetables, and the konbu seaweed becomes soft and silky. You can enjoy a lot of vegetables this way.
Try cooking daikon radish slices (with the sharp edges rounded off) with konbu seaweed, salt, and sugar in a pressure cooker for 10 minutes for a light and mild flavored dish.
Story Behind this Recipe
I thought of a way to efficiently use up the 100 g pack of bonito flakes I use all the time.
Make sure not to simmer the konbu seaweed or bonito flakes longer than necessary. If you want clear dashi, I recommend straining through paper towels. This will make strong dashi, so if you prefer, dilute with 400 ml of water.