Ingredients

6 servings

Preparation

1. Noodles

   Step 1

   Preheat oven to 250°. Spread 1 cup (266 g) baking soda out evenly on a parchment-lined baking sheet and bake 1 hour (baking soda will look exactly the same). Let cool.

   Step 2

   Place 4 cups (500 g) all-purpose flour in the bowl of a stand mixer. Whisk 2 tsp. baked baking soda, 1½ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt, and 1¼ cups water until baking soda and salt are dissolved. Add to flour in three equal additions, mixing to incorporate with a wooden spoon after each addition. Mix until dough resembles a shaggy ball; knead in bowl just to bring dough together. Cover with plastic wrap and let sit at room temperature 30 minutes. (The dough will look a bit dry, but it will relax and hydrate with time.)

   Step 3

   Turn dough out onto a surface and knead until smooth and bouncy, about 5 minutes. Return to bowl and cover with plastic wrap or place in an airtight container. Let rest at room temperature at least 3 hours, or chill up to 12 hours. (If chilling, let dough come to room temperature before making noodles.)

   Step 4

   Cut dough into 6 equal strips (about 123 g each). Working one at a time, flatten strips with your hands until just slightly narrower than the width of the pasta maker. Dust dough evenly and generously on both sides with some of 2 cups (256 g) potato starch or cornstarch to prevent dough from sticking. Roll dough through pasta maker 2 times per setting, starting with the widest setting and narrowing until ⅛” thick. (The dough may feel dry and break apart in the beginning, but don’t get discouraged. Simply fold it onto itself and pass it through the machine again.) Cut sheets of rolled dough into 1-ft.-long pieces.

   Step 5

   Dust sheets of dough with a generous amount of starch and run each through pasta maker on spaghetti setting, gently wrapping noodles around your hand to form a loose bundle as they exit. Carefully set bundles on a parchment-lined baking sheet and sprinkle with more starch to keep noodles from sticking together.

   Do ahead: Baking soda can be baked 1 year ahead; transfer to a jar with a tight-fitting lid and store in a cool place. Noodles can be made 2 days ahead; tightly wrap and chill.

2. Broth

   Step 6

   Combine 5 dried shiitake mushrooms, one 5×2″ piece dried kombu, and 4 quarts water in a stockpot. Let sit at room temperature at least 1 hour and up to 12 hours.

   Step 7

   When mushrooms and kombu are almost done soaking, heat broiler with a rack 5″ from heat element. Remove dark green tops from 1 leek and cut into 2″ pieces; set remaining leek aside. Place leek greens, 2 medium onions, quartered, 5 garlic cloves, smashed, 2 medium tomatoes, quartered, and 2 medium carrots, peeled, cut into 2″ lengths, on a foil-lined rimmed baking sheet. Drizzle with 1 Tbsp. toasted sesame oil and toss to coat. Turn onions and tomatoes cut side up and broil, rotating baking sheet as needed for even browning, until deeply browned across tops, 10–15 minutes. Keep a close eye on the garlic and push to the edges or remove early if starting to get too dark.

   Step 8

   Set stockpot over medium heat and heat until water is just about to come to a simmer. Remove kombu and discard (or reuse to make another round of dashi). Add broiled vegetables, one 2″ piece ginger, scrubbed, sliced ¼” thick, and ½ tsp. black peppercorns to pot and bring to a simmer. Cover and continue to cook at a gentle simmer at least 1 hour and up to 3 hours. (One hour of simmering will result in a lighter, clearer broth, better for spring and summer months. Going longer will result in a deeper, rounder broth, best for fall and winter  months.) Strain broth into another large pot; discard solids. (You don’t want the broth to reduce to less than 3 quarts after straining. If your broth reduces too much, add water as needed.)

   Do ahead: Broth can be made 5 days ahead. Let cool; transfer to an airtight container and chill.

3. Assembly

   Step 9

   Drain one 16-oz. block firm tofu and wrap in a kitchen towel or paper towels; place on a baking sheet. Place a small cutting board or other flat object on top of tofu and let sit 20 minutes. (This will removes excess moisture from tofu before frying.)

   Step 10

   Unpack tofu and cut into 2″ cubes. Place ¼ cup potato starch or cornstarch in a medium bowl. Add tofu and toss to evenly, lightly coat on all sides. Heat ½ cup peanut oil or vegetable oil in a medium skillet with a lid over medium. (Break off a small piece of tofu and drop it in the pan; if it sizzles and makes a crackling sound, you’re ready to fry.) Working in 2 batches, fry tofu, turning occasionally, until golden and crisp, 6–8 minutes per batch. Transfer to a kitchen towel or paper towels on a flat surface and let drain. Sprinkle with 1½ tsp. red chile powder and kosher salt. Set skillet aside.

   Step 11

   Halve and thinly slice reserved white and light green part of leek. Pour off all but 2 Tbsp. oil from reserved skillet and set over medium-low heat. Add leek and a pinch of salt. Cook, stirring occasionally, until softened and lightly brown in spots, about 2 minutes. Reduce heat to low, arrange 6 oz. king trumpet mushrooms, cut lengthwise into ¼”-thick planks, on top of leek. Partially cover skillet and cook 1 minute. Remove lid, increase heat to medium, and cook, tossing, until mushrooms are tender and browned in spots, about 4 minutes. Remove from heat.

   Step 12

   Combine 1 cup soy sauce (preferably usukuchi) and ¼ cup mirin (preferably hon mirin) in a small nonreactive bowl to make shoyu tare.

   Step 13

   Bring broth to a boil. Add 1 cup shoyu tare and 1 tsp. doubanjiang (Sichuan-style fermented chili bean paste) if using. Stir thoroughly, taste, and add up to ¼ more shoyu tare as needed. Taste again and season with more salt and doubanjiang if desired. The broth should be boldly seasoned but drinkable on its own.

   Step 14

   Meanwhile, working in 2 batches, cook noodles in a large pot of rapidly boiling water (no need to salt), spreading out with chopsticks or a spider to avoid clumping, until al dente, about 1 minute.

   Step 15

   To serve, drizzle 1 tsp. of 6 tsp. toasted sesame oil into each bowl. Carefully ladle 1½–2 cups hot broth into each bowl and stir to combine. Using a mesh sieve, scoop noodles from pot and divide among bowls. Top with tofu, leeks, and mushrooms, then bite-size pieces blanched seasonal vegetables (such as peas, snow peas, spinach, kale, asparagus, and/or fava beans) if using. Scatter some thinly sliced scallions over and tuck a square of toasted nori sheet into each bowl. Serve with toasted sesame seeds alongside for topping if desired.