Dashi is a soup stock used extensively in Japanese cuisine. Traditionally, the stock is made with bonito (fish flakes); this vegetarian version combines shiitake mushrooms with kelp (dried seaweed or konbu) to impart a similar robust flavor. These two ingredients are strained, leaving a clear broth void of calories, fat, and other nutrients (that's why there's no nutrition information below).If you are in a pinch for time, substitute commercial mushroom broth (such as Pacific Natural Foods Organic Mushroom Broth) for the dashi, since the overall flavor is of mushrooms, not kelp.
Place 8 cups water and mushrooms in a Dutch oven; bring to a boil. Reduce heat, and simmer 45 minutes. Add the remaining 1/2 cup water and kelp; bring to a boil. Remove from heat. Drain mixture in a colander over a bowl, reserving mushrooms for another use; discard kelp. Store dashi in an airtight container in the refrigerator.