1 large onion, peeled and halved
2-inch piece fresh ginger root, peeled and halved lengthwise
3-inch cinnamon stick, preferably Vietnamese cassia-cinnamon
1 star anise
1 teaspoon coriander seeds
4 cups unsalted vegetable stock
2 teaspoons soy sauce
4 carrots, peeled and coarsely chopped
1/2 pound dried flat rice noodles
Vegetables such as bok choy, napa cabbage, or broccoli
For the Broth
Char onion and ginger over an open flame (holding with tongs) or directly under a broiler until slightly blackened, about 5 minutes on each side. Rinse with water.
In a large pot, dry roast cinnamon, star anise, cloves, and coriander over medium-low heat, stirring to prevent burning. When spices are aromatic, add vegetable stock, soy sauce, carrots, and charred onion and ginger.
Bring broth to a boil, reduce heat, and simmer, covered, for 30 minutes. Strain and keep hot until ready to serve.
For the Noodles
While broth is simmering, place noodles in a large bowl and cover with hot water. Let stand for 20-30 minutes or until tender but still chewy. Drain. (If soaking does not soften the noodles enough, blanch them in a pot of boiling water for a few seconds.)
For the Toppings (optional)
While broth is simmering, prepare toppings as desired. Toppings should be unseasoned or only lightly seasoned so as not to interfere with the flavor of the broth.
1/2 onion, very thinly sliced
2 scallions, thinly sliced
1 chile pepper (Thai bird, serrano, or jalapeño), sliced
1 lime, cut into wedges
1/2 cup bean sprouts
Large handful of herbs: cilantro, Thai basil, culantro/saw-leaf herb
Hoisin sauce, sriracha (optional)
Divide noodles between two bowls. Arrange toppings over noodles. Ladle about 2 cups of broth into each bowl. Serve with garnishes on the side, which diners should add to taste.