In a 2-cup (500 ml) glass measuring cup, submerge the dried shiitake mushrooms in 400 ml warm water for 20-30 minutes. Weigh them down to keep them submerged. After 30 minutes, squeeze their water back into the cup, then slice the mushrooms. Reserve the soaking liquid; use 1 cup (250 ml) of it in the stock mixture, not all the soaking water.
