Broth
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
2 cloves
1 teaspoon coriander seeds
4 cups unsalted vegetable stock
2 teaspoons soy sauce
4 carrots, peeled and coarsely chopped
Noodles
1/2 pound dried flat rice noodles (known as bánh phở; use 1/16", 1/8", or 1/4" width depending on availability and preference)
Toppings (optional)
Protein such as fried or baked tofu, bean curd skin, or seitan
Mushrooms
Vegetables such as bok choy, napa cabbage, or broccoli
Garnishes
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)