1. Use a mortar and pestle to pound coriander roots, garlic, peppercorns and salt to a rough paste (you could also do this in a food processor).
2. Heat oil in a pot just large enough to hold the chicken. Fry paste for 1 minute or until fragrant. Add the whole chicken and lightly brown for about 2 minutes per side. Add dark soy sauce, fish sauce, star anise and cinnamon sticks. Pour in enough water to almost cover the chicken.
3. Bring to a boil, turn the heat down to medium-low, cover and simmer for 60 minutes, turning the chicken over halfway through cooking.
4. Carefully remove chicken and place into a deep serving dish. To the broth, add fish sauce to taste and sugar. Pour broth over chicken and garnish with coriander leaves and sliced chillies. Serve with steamed rice.