To make the curry paste, gradually combine all the ingredients, except the shrimp paste, using a pestle and mortar. Add the ingredients one at a time and pound vigorously after each to form a rough paste. Add the shrimp paste and continue to pound together until you have a smooth paste. The paste is ready when you can no longer identify any of the ingredients. Will keep in an airtight container in the fridge for 3-5 days or in the freezer for up to three months.
To make the curry, heat the oil in a saucepan over a low heat. Add the green curry paste and stir until fragrant – you won't need all the paste. Increase the heat to medium and add in the chicken pieces, coating with the paste. When the chicken has browned, spoon in half the coconut milk, avoiding adding any of the water at the bottom of the tin – this will split the curry. Stir continuously for 10 mins or until the chicken is fully cooked and the sauce is simmering.
Pour in the remaining coconut milk, discarding the water, and turn the heat up to bring to the boil, then return the heat to medium. Add the Thai and pea aubergines with the baby corn and sugar snap peas and simmer, stirring occasionally, for about 10 mins or until the flavours combine, the sauce thickens slightly and vegetables are tender.
Gradually add the fish sauce and palm sugar, stirring and tasting after each addition until you are happy. Add the lime leaves and most of the Thai basil, then cook for a further 5 mins to let their flavours infuse. To serve, pour the curry into individual serving dishes and scatter over the sliced chilli and the remaining Thai basil leaves.