Heat the oil in a saucepan over moderate heat and fry 3 of the chillies, the cardamom and the curry leaves for 1 minute (apparently be careful if using fresh curry leaves as they spit). Add the onion and sauté until golden then add the garlic, ginger, curry powder and other spices. Stir-fry for 1 minute. Add the lamb, tomato paste and water, mix well and cook on high heat for 10 minutes, scraping the bottom of the pot from time to time. Cover and simmer on low heat for 1 hour, stirring occasionally.
Add the coconut milk and lemongrass. Turn up the heat and bring to the boil, stirring. Reduce the heat and add the tamarind. Mix well, cover and simmer for a further 30 minutes. Add the remaining curry leaves and chillies.
Burmese curry powder
In a heavy-based pan over low heat, dry-roast separately the coriander, cumin, fenugreek and fennel, stirring constantly until each becomes fairly dark brown, but do not let them burn. Set aside.
Using a blender on high speed process all the ingredients until ground to a fine powder. Transfer to airtight container.