Marinate the lamb with all the spices, salt, yogurt, mint, ginger/garlic, tomato paste, lemon juice and mint. Refrigerate overnight or for an hour.
In a large pot heat the butter ghee. Add the fennel seeds and once it splutters add the whole spices, cinnamon stick, bay leaf, black cardamom and green cardamom. Fry until fragrant
Add the curry leaf, onion, thyme and green chillies. Fry until onion is golden brown
Add the marinated meat. Season with salt and bring to a boil
Lower the heat, cover and simmer. After 45 minutes add the fresh cream (if using) and simmer further until meat is tender and gravy thickens. You can add a pinch of sugar if sauce is too acidic
In between cooking you can add a little water if you prefer for more gravy
Serve with rice or naan bread