Dry roast 2 tsp of the cumin seeds until dark brown. Set aside.
Heat oil in a pan, add remaining cumin seeds. When they begin to crackle, add the onions and fry until soft. Add chicken and brown. Add garlic and ginger and fry for 3-4 mins. Add tomatoes, turmeric, chilli, salt, garam masala and 2 tbsp coriander leaves. Stir, cover and simmer for 30 mins. Add a little water if mixture seems too dry. Continue cooking until the chicken is tender and the gravy is thick.
Coarsely pound the dry roasted cumin and sprinkle onto the hot gravy with the remaining coriander. Rest for 5 mins before serving.

Goes well with Spicy Fried Potatoes.