Heat oil and ghee in the heavy bottom pot to medium heat. Add onions and sautee for 1-2 minutes until translucent. Add ginger, garlic paste and continue stir until the onions are brown.
Next add the tomato passata and cook until the tomato change colour and oil separates. Add turmeric, chilli powder, garam masala, coriander powder and cumin powder. Stir it well for a few seconds.
Pour in water and 3tbsp double cream. Season with salt to taste and bring it to simmer.
Placed the grilled lamb back in the sauce, close the lid and cook with low-medium heat for one and half hours or until the meat is tender. Stir occasionally and add more warm water if needed.
Add the rest of cream and cook for another 1-2 minutes. Turn off the heat and stir in chopped coriander.
Serve with basmati rice, naan, or chapati.