A Japanese stock made with kombu (dried kelp) and dried shiitake mushrooms. This stock can be made quickly, but is best when the ingredients are given more soaking time.
Place the water, mushrooms, and kombu in a glass jar, cover the jar, and soak at room temperature for at least 30 minutes, preferably for 1 to 4 hours. You can also soak everything in the refrigerator---soak for a minimum of 4 hours up to 12 hours.
After soaking, remove the mushrooms and kombu and set them aside for use in another recipe, or discard them.
Pour the dashi (stock) through a fine-mesh strainer, or a strainer lined with 3 layers of cheesecloth, into a clean container, to remove any debris that may have settled at the bottom of the jar.
Pour the dashi back into the jar and place in the refrigerator until you are ready to use it. This dashi can be stored in the refrigerator for several days.