In a large mixing bowl combine all of the ingredients for the lamb koftas, except the oil for cooking, and mix well with the hands. Form into golf ball sized balls (the mixture should make about 20 koftas).
Warm a little oil in a frying pan over a medium heat then add the koftas and brown on all sides. Remove from the heat and set aside.
For the curry:
Warm the peanut oil in a large heavy bottomed pan over a medium heat. Add the minced ginger, onion, chilli and garlic and cook and stir for 3 to 5 minutes. Add the turmeric, cumin, coriander, cayenne and salt and mix well. Stir in the tomato puree and cook until the sauce begins to thicken, about 6 to 8 minutes.
In a food processor blend the cashew nuts with a little of the cream until they become a paste. Add to the sauce along with the remainder of the cream and the tomatoes. Cook and stir for 5 minutes then add the garam masala and the lamb stock. Finally add in the koftas and reduce the heat to low. Continue to cook for 30 to 40 minutes until the koftas are no longer pink in the centre. Sprinkle with chopped fresh coriander and serve with rice or naan bread.