In a food processor, add the lamb, ginger, fennel, garam masala, cumin, cardamom and salt. Grind the spice mixture until smooth.
Divide and shape the meat mixture into two ounce portions. Refrigerate until ready to use.
Heat the oil in a large saucepan over medium-high heat. Add the cinnamon stick and cumin seeds and onion cook the onion until golden brown, about 10 minutes. Add the paprika and the salt and fry for 30 seconds. Stir in the tomatoes, remove from heat and slowly stir in the sour cream.
Carefully add the chilled meat balls and bring it to a boil .Simmer uncovered, for 30 to 40 minutes, over very low heat. Add ½ cup of water. Cook until the meat balls are very tender and the sauce is thick. Serve garnished with cilantro leaves.