Make the curry paste by mixing together all the ingredients in a large bowl – for a milder curry remove the seeds from the chillies before chopping them finely. Add the lamb and potatoes and combine well.
Heat the oil in a heavy-based pan or casserole and tip in the meat and potatoes. Use a wooden spoon to stir-fry for 6–8 minutes. Pour in the chopped tomatoes and 150 ml (¼ pint) water, bring to the boil and season well then allow to bubble gently for 20–25 minutes until the potatoes are cooked and the lamb is tender.
Serve accompanied with toasted naan bread and a bowl of Greek yogurt, if liked.