Add the onions and the cinnamon stick and sauté until the onions turn golden (5-8 minutes).
Add garlic and cook for another 4 minutes.
Add ginger, tomatoes and your spice mix (salt, black pepper, turmeric, cumin, coriander, garam masala and cayenne). Cook for 5 minutes or until the oil separates.
Now in with the chicken:.
Skin the chicken rinse them (you can do this while the masala cooks).
Add chicken to the masala, turning and coating the pieces well.
Cook for 10 minutes, until the chicken starts to brown.
Stir in the sour cream and water and increase the heat to medium-high.
Wait for a boil, reduce heat and cover. Cook for 15 minutes or until chicken is completely cooked, being sure to stir the pot a few times.
When your chicken is cooked, remove the pan from the heat. Fish out the cinnamon and let your food cool for 30 minutes or more. Remove the chicken from the pot and its meat from its bones before adding the meat back into the masala.
Before serving, heat it all up again on medium heat until it starts to simmer. Remove from the heat, stir in cilantro.