Cut the chicken into pieces and brown in oil. Remove and add chopped onion. Saute until tender.
Add garlic and ginger, make sure there is enough oil so that nothing sticks. Add cumin and mustard seed. Fry until the mustard seeds begin to "pop".
Add the turmeric and curry powder and stir constantly to prevent any sticking. Stir the "paste" until the curry powder becomes fragrant; this usually takes 1 to 2 minutes (be careful not to burn the curry powder).
Add the chopped tomatoes and stir until they form a sauce (3-4 minutes). Add the chicken broth, cinnamon stick and chicken. Cover and simmer until chicken is cooked.
Stir in the garam masala garnish with chopped fresh celantro leavs and serve with white rice.