Rub duck or chicken with five-spice powder and brown in a very hot pan with a little oil. Place in a deep pot with lemon grass, shallots, garlic, ginger, star anise and mushrooms (with water). Add chicken stock and simmer for 1 ½ hours. Remove duck or chicken. Add fish sauce, black fungus, and season if required. Mix corn flour with a little water and add. Bring to the boil to thicken the sauce.Return duck or chicken and simmer uncovered for 20–30 minutes. Add spring onions and serve with rice, garnished with mint.