Put the mutton to marinate overnight or for at least 3 hours.
Heat the oil in a heavy bottomed pan
Add the sliced onion and gently fry until brown and caramelised. Once the onion is browned remove from the pan with a slotted spoon and reserve for later.
Add the curry leaves, cinnamon and star anise to the pan (careful they may splutter)
Add the onion puree and 1 tsp of salt. Continue to fry gently for 15 minutes
Add the garlic and ginger and fry gently for 30 seconds
Add the curry Masala and fry for 20 – 30 seconds
Add the mutton and any marinade, stir and let seal
Add the watered down tomato puree, stir and let reduce back down to a thick paste.
Add the blended tinned tomatoes and chillies. Bring back to a simmer
Add the yoghurt and cashew paste, stir and again bring back to the simmer.
Turn the pan down and cover with a lid. Either cook on a very gentle heat on the hob (use a heat diffuser if you have one) or cook in the oven on a low temperature around 140°C. It wants to cook for around 2 ½ - 3 hours. If the sauce is looking to thick after an hour of cooking then you can thin it with a little water.
After 2 ½ - 3 hours you can add all the other ingredients, including the caramelised onions from earlier (keep a few almonds and coriander leaves back to garnish if you wish). Cook for another 20 – 30 minutes on the hob, lid off, before serving with pilau rice & Indian style breads.