Dry-roast the coriander in a small frying pan for 1 minute until fragrant, then remove and dry-fry the cumin.
Using a mortar and pestle, pound the chillies, lemongrass, galangal and lime skin or leaves into a paste. Add the garlic, shallots and coriander roots and pound together. Add the remaining ingredients and dry-roasted spices one at a tim