As a source of umami, dashi is even more elemental to Japanese cooking than parmesan or anchovies are to Italian cooking or chicken broth is to Western cooking in general. Dashi is a broth made of kombu (dried kelp) and shavings of katsuobushi, which is commonly referred to as dried bonito in English, but is actually dried, fermented and smoked skipjack tuna. There are as many subtly different versions of dashi as there are Japanese cooks and not surprisingly, Japanese chefs think very hard about small variations in the quality of the ingredients - "Western water is no good for dashi!" - as well as temperatures and techniques - "don't stir!". For my recipe, I have settled on a version I learned from Chef Yorinobu Yamasaki of NYC's excellent Donguri restaurant.
With just two widely available ingredients other than water, making a respectable dashi is straightforward and quick. It definitely beats boiling bones for many hours to make bone broth. Dashi is best the day it's made but will keep a few days in the fridge. I've never had a problem using up fresh dashi since it's so versatile. If you enter dashi into the search window on my site, you will find a number of possible uses and if these seem like too much of a production, you could always throw together a delicious clear soup in minutes, adding to the dashi a splash of soy sauce, a pinch of salt and anything from thinly sliced vegetables or shiitake mushrooms to whole cherry tomatoes or diced tofu. I also keep a few dashi ice cubes in my freezer in an airtight Ziploc bag for occasions when I only need a small quantity.
Making dashi (yields about 6½ cups):