Preheat 450 ml of cooking oil, fry potatoes until half-cooked, drain and set aside for later use.
Put onion, shallot, garlic, old ginger, galangal, lemongrass and cooking oil into blender, process until smooth.
Pour the mixture into cooking pot, add in curry powder and mix well.
Heat up curry paste over medium heat, then reduce to medium-low heat and cook until fragrant (about 5-6 minutes).
Add in chicken pieces, turn to medium heat, cook until the outer parts are cooked.
Add in potatoes, mix well.
Add in thin coconut milk (or plain water), mix well.
Add in star anise, green cardamom and curry leaf (optional: to enhance the flavour of curry).
Mix 2 tsps of water with asam paste, add in.
Bring to the boil, reduce to low heat, cover and cook for 25-30 minutes, until all ingredients are tender, stir 1-2 times in between cooking.
After 30 minutes, discard some chili oil using a strainer if you prefer a less oily curry.
Add in thick coconut milk, evaporated milk and salt, mix well.
Bring to the boil again, then OFF the heat.