Heat the oil in a large pot over medium-low heat and add the curry leaves, fenugreek seeds, 1 tablespoon of the Jaffna curry powder, cardamom pods, cloves, and cinnamon stick. Stir for 30 seconds and then add the chopped onion. Cook for 10 minutes or so until golden in color.
Increase to high heat and add the garlic and ginger that has been pounded into a paste-like consistency. Add the bruised lemongrass and the cut lamb. Once the lamb pieces are browned, add the other tablespoon of Jaffna curry powder, chili powder, turmeric, and tomato paste. Stir and sauté for 2 minutes. Reduce heat to low, cover, and cook for 30 minutes, stirring occasionally.
Add the coconut milk and simmer uncovered for 15 minutes, until the sauce is rich and thickened. Add salt to taste. Adjust seasoning. Take out lemongrass and cinnamon stick. Serve with hot basmati white rice.
