Mushroom Udon Noodle Bowl. Pic by Karsten Moran for The New York Times.
4 to 6 servings

For the broth

3 large scallions, trimmed

1 handful dried shiitake mushrooms, crushed (about 1/2 cup)

1/4 cup crumbled dried seaweed, such as kombu or dulse (optional)

1 (2,5 cm) chunk of ginger, smashed and unpeeled

2 whole, unpeeled garlic cloves

Stems or trimmings from fresh shiitake mushrooms (optional)

1 teaspoon salt

For the soup

450 g dried udon noodles (or use fresh or frozen, cooked udon)

2 tablespoons butter

1 cup chopped leeks, white and pale green parts only

225 g  fresh shiitake mushrooms, stems removed, caps sliced in 2 and a half cm strips (save trimmings for broth)

1 teaspoon minced ginger

2 cloves garlic, minced

1/4 cup mirin or dry sherry

1/2 teaspoon sesame oil

2 tablespoons soy sauce

2 cups chopped bok choy

1/2 cup red or white miso

1 cup soft or medium tofu, cut in small cubes

4 scallions, finely chopped, for garnish

Shichimi togarashi or crushed red-pepper flakes, for garnish

Method

Make the broth: In a large pot, bring 8 cups water to a boil over high heat. Add scallion, dried mushrooms, seaweed (if using), ginger, garlic, fresh mushroom trimmings and salt. Reduce heat to a gentle simmer and cook for 20 minutes. Strain and set aside.

Meanwhile, in a separate pot, cook udon noodles until al dente, then drain, rinse well with cold water, and keep at room temperature.

In a soup pot, melt butter over medium-high heat and swirl to coat the bottom of the pot. Add leeks and sliced shiitake and cook, stirring, until softened, about 2 to 3 minutes. 

Add ginger, garlic, mirin, sesame oil and soy sauce and cook for 1 minute. 

Turn heat to high, add reserved broth and bring to a simmer.

Add bok choy and reserved noodles and cook for 1 to 2 minutes, until greens are cooked and noodles are heated through. 

Gently stir in miso and tofu. Turn off heat.

Using tongs, divide noodles among 4 to 6 bowls. Ladle hot soup over noodles. Sprinkle with scallions and serve. 

Pass togarashi or crushed red pepper at the table.