- 4 ounces soba (Japanese-style noodles)
- Kosher salt
- 2 tablespoons white miso
- 1 tablespoon fresh lime juice
- 3/4 teaspoon toasted sesame oil
- 3 serrano chiles, 2 halved and seeds removed, 1 thinly sliced
- 1 garlic clove, peeled
- 2 scallions, white and pale-green parts only, chopped
- 2 cups chopped basil leaves, plus torn leaves for serving
- 2 cups chopped cilantro
- 2 cups trimmed watercress
- Toasted sesame seeds (for serving)
- Cook noodles in a large pot of boiling salted water until al dente, about 5 minutes. Drain, reserving 1/4 cup soba cooking liquid.
- Meanwhile, whisk miso, lime juice, and oil in a large bowl. Chop halved chiles, garlic, and a pinch of salt together on a cutting board, then use the side of chef’s knife to mash into a paste. Transfer to bowl with miso mixture and mix well. Add scallions, chopped basil, and cilantro and toss to combine; season pesto with salt.
- Add soba, watercress, and sliced chile to pesto and toss, adding reserved soba cooking liquid by the teaspoonfuls as needed, until nicely coated.
- Serve noodles topped with torn basil and sesame seeds.