Rich-tasting mushroom broth gives this soup its hearty flavor, though any vegetarian broth will work here.
1. Place noodles in large bowl, and cover with boiling water. Let stand 5 minutes, or until noodles are softened.
2. Meanwhile, bring mushroom broth and 4 cups water to boil in large pot. Add leeks and lemongrass, reduce heat to medium-low, and simmer 12 minutes. Stir in tofu, soy sauce, brown sugar, ginger, and garlic-chile sauce, if desired. Simmer soup 5 minutes more.
3. Drain noodles, and divide among 4 soup bowls. Ladle soup over noodles, and top with bean sprouts, cilantro, basil, mint, and peanuts, if desired.