Adapted from Elizabeth Andoh's Washoku: Recipes from the Japanese Home Kitchen (Ten Speed Press 2005).
This simple recipe for a dashi, or homemade stock, requires kombu (seaweed) and bonito flakes (dried, shaved fish), both readily available at Asian food markets and other stores across the country.
Dashi (Basic Sea Stock)
Makes about 1 quart
15 to 20 square inches kombu
4 1/4 cups cold water, preferably filtered or spring
1/2 cup loosely packed bonito flakes
Andoh recommends shiro miso because it's mild and somewhat sweet. But she says you can use any kind of miso in this soup recipe, so if you already have some (ahem) unopened in your fridge, now's the time to crack it open.
1 package enoki mushrooms, about 3 ounces, trimmed
2 watercress sprigs or 2 scallions
3 1/2 cups dashi
1/2 block extra-firm tofu, diced
3 tablespoons miso
Place the kombu in a pot with the water. To draw out maximum flavor and nutrients, let soak for 10 to 15 minutes before turning the heat on to medium.
Remove the pot from the heat as soon as small bubbles begin to break on the surface and at the edge of the pot. Add the bonito flakes, scattering them across the surface of the water. After several minutes, the flakes will begin to sink. The larger the flakes, the longer they'll take to sink. Within 3 to 4 minutes of adding the fish flakes,
pour the stock through a fine strainer lined with cheesecloth or a doubled-over paper towel.
If you're not using the dashi right away, it will keep in the fridge for a few days. (Andoh says it doesn't freeze well.) Let it cool before covering it tightly and putting it away.
Signs of spoilage include a sweet smell (rather than a smoky one), a film forming on the surface or around the edges of the container, or stickiness when pouring.
Cut the trimmed mushrooms into thirds. Place the pieces with the caps directly into individual soup bowls and the remaining stem portions into a pot.
Chop the leaves and stems of the watercress coarsely. If using scallions, trim away the root and cut both the white bottoms and green tops into thin circles. Divide the garnish among the bowls.
Add the dashi to the pot holding the mushroom stems and bring to a boil over high heat. When the stock begins to boil, skim away any froth and reduce the heat to maintain a steady but not vigorous simmer. Add the tofu and cook for 1 minute.
Just before serving, place the miso in a bowl, add some of the hot stock from the pot, stir to mix, then pour this through a fine-mesh strainer into the soup. (This will keep out the miso solids so the soup is clear, not grainy.)
Ladle the soup into the bowls that hold the enoki caps and garnish, and serve immediately.