Preparation: Trim lemongrass stalks, discarding all but the bottom third. Cut into 3-4 inch lengths and smash lightly with a heavy knife. Mince Thai chilis (if using), removing seeds and/or ribs as desired. Cut the ginger into thirds. Cut or rip kaffir lime leaves into large pieces. Make the rice vermicelli according to package instructions and leave aside in separate bowl.

In a medium to large pot or dutch oven add stock, ginger or galangal, lemongrass, lime leaves, and half the chilis. Bring to a boil, reduce heat to medium and add coconut milk, bringing only to a gentle simmer. Do not boil coconut milk - it might separate. Add the chicken and simmer until cooked through, 3-5 minutes. Fish out and discard the ginger and lemongrass. Or you can leave them in, but don't serve them.

When chicken is done add fish sauce, straw mushrooms, lime juice, the rest of the chilis, and sugar and simmer for 5 minutes. Place some vermicelli in bowls and ladle soup on top. Serve topped with chopped cilantro and/or Thai basil.