Vegetarian Udon Noodle Soup

Cook noodles according to package directions; drain and set aside.

Meanwhile, heat oil in a large pot over medium heat. Add garlic, ginger, and serrano; cook until fragrant, about 1 minute. Add broth, mirin, and 1 Tbsp. soy sauce; bring to a simmer. Stir in mushrooms and carrots; simmer until the carrots are just tender, 3 to 6 minutes. Stir in bok choy and cook until the vegetables are tender, about 2 minutes more.

Whisk warm water and miso in a small bowl until smooth; add to the pot. Stir in tofu and cook until heated through, about 1 minute.

Stir scallions into the soup. Divide the noodles among 4 bowls. Ladle the soup over the noodles. Drizzle each bowl with 1 tsp. toasted sesame oil and 1/4 tsp. of the remaining soy sauce.