For curry paste, finely grind spices with a mortar and pestle. Add remaining ingredients in order of toughness with ½ tsp salt, pounding them to a paste (alternatively, blend in a food processor until smooth, but the mortar and pestle will give you better colour and fragrance).
Heat lard in a large wok or saucepan over medium heat. Add curry paste and the head of coconut cream skimmed from top of can, and stir until fragrant and oil separates (12-15 minutes). Add coconut milk and simmer over low heat until thickened (30 minutes). Increase heat to high, add chicken and stock, cover with a lid and simmer, stirring occasionally, until chicken is cooked and flavour deepens (30 minutes). Add fish sauce, seasoning to taste, and stir in palm sugar and remaining coconut cream.
Increase heat to medium, then drain eggplant, add to wok, and simmer until tender (5 minutes). Remove from heat, stir in lime leaf, chilli and basil, and serve with rice.
