1.Place noodles in a bowl and cover with cold water. Soak for 10 minutes. Drain and set aside.
2.In a saucepan, Place chicken stock, water, lemongrass, eschalot, lime leaves, dried chilli, galangal and coriander roots on high heat. Bring to boil. Reduce heat to low and simmer 10 minutes. Add noodles for last 2 minutes of cooking.
3.Add fish and mushrooms and cook for another 3-4 minutes, until just cooked. Add fish sauce, lime juice and brown sugar to taste. Serve garnished with coriander leaves and fresh chilli.