1. Heat the oil and butter in a large saucepan.
2. Add the onions and cook for 2-3 minutes, then add the garlic, ginger, chilli, cardamom, cumin, turmeric, garam masala and ground coriander. Cook over a medium heat until the onion is soft and the spices are cooked.
3. Add the potatoes and cook for 3-4 mins.
4. Add the stock and bring to the boil. Season to taste with salt and freshly ground black pepper. Reduce the heat and simmer for 10-15 minutes, until the potatoes are tender.
5. Stir in the yoghurt and cream, then add the lemon juice.
6. Add the cooked turkey, fold in and simmer to heat through. Sprinkle with coriander leaves and serve immediately.