This variation of kombu dashi (or konbu dashi) is a more savory, stronger tasting soup broth. You can also make dashi, or stock, from katsuobushi (dried fish flakes) and niboshi (dried anchovies/sardines). There is kombu (a thick, dried kelp) that is available specifically for making dashi called kombu dashi.
6 cups of cold water
1 strip of dried kelp, about 5-6" inches (kombu こんぶ)
4 dried shiitake mushrooms
Soak shiitake mushrooms and kelp (kombu) in 6 cups of cold water for 30 minutes. (If you plan on using shiitake mushrooms in the dish you are making, soak for 2-3 hours).
Remove the mushroom stems, then slice the caps thinly. Put the slices back into the water.
Bring all of it to a simmer; simmer for 5 minutes.
Remove the kombu, then let the mushroom slices simmer for another 10 minutes. Remove the mushroom slices before using the broth.