Fresh aromatics, a mortar and pestle and a little muscle are the keys to an authentic green curry.
The traditional way to make a curry paste is to pound the aromatics using a mortar and pestle, starting first with the chillies and then adding each ingredient separately, from hardest to softest, and pounding it to a pulp before adding the next.
Use a mortar and pestle with generous depth and diameter, as well as a bit of heft. A mortar of 12cm-15cm diameter is ideal. And it should have a rough-textured interior, such as granite.
If you don't have a mortar and pestle, David Thompson says the next best thing is a blender, but definitely not a food processor. The four blades of a blender cut and purée the ingredients quickly to form a paste (you may need to do this in batches, adding a little water, but never oil, to loosen it and prevent the machine from overheating), whereas the two blades of a food processor take longer and only achieve a coarse consistency.
Prepare all the fresh ingredients before you start to pound the paste: chillies should be de-stemmed; lemongrass trimmed and peeled back to its tender pale centre; kaffir lime rind removed and pith discarded; coriander roots scraped and soaked to remove dirt. Use old but not dry galangal, but if what you have is on the wizened side, soak it in salted water for five minutes to soften slightly before peeling. The turmeric, too, needs to be peeled. Then chop each ingredient, the finer the better, and set them aside separately.
Cumin and coriander seeds should be dry-roasted and ground before they're added to the curry paste, while whole white peppercorns are used unroasted.
A pinch of salt is also often added during the pounding process. This acts as both an abrasive and a preservative, but be careful not to over-salt at this stage.
The recipe here makes more paste than you need for a single batch of curry, because it's almost impossible to obtain the fine texture you're after with a smaller quantity. It will last up to a fortnight covered directly with a piece of plastic wrap and refrigerated.
The next task is to fry the paste to release and develop its fragrance. For a coconut-based curry, such as the green curry here, the paste is fried in coconut cream, which first needs to be cracked or simmered over a very low heat until the oil floats to the top. Add a little coconut oil to the coconut cream before simmering; or fry the curry paste in a little coconut oil, then add the coconut cream; or use a better organic coconut cream, such as Spiral Foods, that is more likely to crack. Stir the paste regularly to prevent it from burning. The colour deepens, the fragrance intensifies, and the paste may begin to look scrambled; this signals that the paste is flavoursome and sufficiently cooked.
Add the chicken at this stage, stir to coat well, then season with fish sauce. Many Thai dishes are also seasoned with sugar. Having tried it both with and without palm sugar, it seems to be a matter of personal taste: people with a higher tolerance for chilli heat preferred the unsweetened curry, while those with a lower tolerance preferred the sweetened one. Only the merest hint of palm sugar is necessary, as the main flavour profiles of a green curry should be hot and salty.
Additional liquid comes in the form of coconut cream or stock, or a combination of the two (a green curry is much thinner than a red curry), while texture comes with crunchy vegetables. A handful of Thai basil and a few bruised kaffir lime leaves add gorgeous fragrance, while slices of long red chilli kick up the heat.