First make the cashew cream. Soak the cashews in 200ml water for 30 minutes.
Transfer the cashews and their water to a blender with the lemon juice and blend until smooth. Store in the fridge for up to 1 week. The cream may thicken slightly when cold – simply thin it out with a little water if necessary.
Then make the curry paste. Put the coriander, onion, garlic, chilli, ginger, lemongrass (if using) and lime zest into the bowl of a food processor and blitz until finely chopped.
Heat the olive oil in a large saucepan and fry the paste for 3–4 minutes, stirring all the time.
Add the coconut milk, the black beans and their liquid and 200ml of water and simmer for 5 minutes to allow the flavours to infuse.
Stir in the cashew cream and vegetables. Mix well and simmer for 5–7 minutes until the vegetables are tender but still a little crunchy.
Finish the curry with the fish sauce and squeeze over the reserved limes. Season to taste with salt and pepper and serve.
