Place all the curry paste ingredients in a food processor and blend into a smooth paste.
Heat a drizzle of oil in a large frying pan on a medium heat. Add ¾ cup of the curry paste (freeze the remaining paste if you like, for another curry) and fry for about 4 minutes until very fragrant, stirring continuously to prevent sticking.
Add another drizzle of oil, the onion and a pinch of salt and cook until onion is very soft (about 5 minutes). Add 1 Tbsp water if mixture begins to stick to pan.
Add chicken and fry for 8-10 minutes or until lightly golden. Add coconut milk, soy sauce and kaffir lime leaves and simmer for about 8 minutes until chicken is cooked through and sauce has intensified in colour and thickened slightly. Season to taste with lime juice.
Garnish with extra roasted cashews and thinly sliced red chilli and kaffir lime leaf. Serve with rice, with a handful of beansprouts, diced cucumber and a lime wedge on the side.