Make the curry paste by processing all the paste ingredients together to a fine paste. If you have time, I recommend doubling or tripling the recipe and freezing the paste in portions for later use.
Heat the oil in a large casserole dish and fry the paste for 5-10 minutes until it is colored and fragrant, stirring frequently so that it doesn’t stick to the bottom.
Add the lamb shanks to the paste and oil and lightly brown on all sides. Add all the remaining ingredients to the pot, bring to the boil and simmer covered for about 1.5 hours, stirring occasionally. Remove the lid and simmer for a further 1 to 1.5 hours until the meat is very tender, pulls away easily from the bone, and the liquid has reduced to a thick gravy.
Cover the curry and allow it to cool on the stove. Refrigerate overnight if possible. Reheat and adjust seasoning before serving. Serve with white rice and sliced cucumbers.