- ¾ ounce dried shiitake (about 10 small)
- 2 whole star anise “flowers”
- 2 cups boiling water, plus 4 cups additional water
- 1 tablespoon peanut oil (Loriva brand roasted is especially good)
- 5 scallions, thinly sliced (keep white and green parts separate)
- 1 cup finely diced onion
- 2 teaspoons minced garlic
- ¼ cup dry sherry
- 1½ cups split peas, picked over and rinsed
- ½ teaspoon salt
- 5-inch chunk fresh ginger (about 4 ounces)
- 2 to 3 cups loosely packed watercress leaves (from 1 average bunch)
- 1 to 3 tablespoons Japanese soy sauce (Shoyu or Tamari)
- 1½ to 3 teaspoons Asian (toasted) sesame oil (optional)
- 1 tablespoon toasted black sesame seeds, for garnish (optional)
- Place the shiitake and star anise in a large glass measuring cup and pour the 2 cups boiling water over them. Cover and set aside until the mushrooms are tender enough to cut, usually about 10 minutes. Lift out mushrooms and star anise with a slotted spoon. Slice the caps thinly, discarding any stems (they are too woody to eat) as you go. Set the shiitake, star anise, and soaking liquid aside.
- Heat the oil in a large soup pot. Add the white part of the sliced scallions, the onion, and the garlic, and cook over medium-high heat, stirring frequently, until they soften slightly, about 2 minutes. Add the sherry and cook over high heat, stirring constantly, until the sherry evaporates, about 30 seconds. Add the 4 cups of water, split peas, sliced shiitake, star anise (discard any broken pieces), and salt. Pour in the shiitake soaking liquid, taking care to leave behind any grit on the bottom of the cup.
- Cover and bring to a boil. Cook at a gentle boil, stirring from time to time, until most of the peas have lost their shape, 50 to 60 minutes (or longer if the split peas are old and dried out). Taste the soup from time to time and remove the star anise if you feel it has given off sufficient flavor.
- While the soup is cooking, prepare the ginger juice: trim and grate the ginger. Once you have about a tablespoon, press to grate ginger, use a porcelain grater, available in Asian groceries, or the side of a box grater with rice-sized holes. Better yet, use the terrific rasp sold for grating cheese, available from Cooking by the Book, inc. (212-966-9799). It’s not necessary to peel ginger before grating it, but do peel before mincing.