Heat oil in a wok over medium heat, then add onion, ginger, garlic, cinnamon, star anise, cardamom seeds and curry leaves and stirfry until fragrant and onion is soft (about 3 minutes). Add 1.5 litres of water and bring to the boil, add curry powder, ground chilli and sugar and stir to combine. Add chicken, potato and lemongrass, return to the boil, then reduce heat to low and simmer until chicken and potato are cooked through (about 15 minutes). Scatter with chilli and serve with rice.
Note Look for finely ground mild (meat) Indian curry