Heat a large frying pan with 1 tbsp oil. Drain the meat, saving the marinade. Season well then sear, about 2 minutes on each side, until browned. Remove from the pan and add 2 tbsp oil, the onion and garlic. Cook until soft, about 10 minutes, on a medium-low heat. Add the meat with the reserved marinade, tomato purée, vinegar, chilli powder, turmeric and cinnamon sticks. Add 400ml water and stir. Cover with a lid and cook on a very low heat for 1½-2 hours. The meat should be falling-apart tender. Taste for additional vinegar, salt or sugar. Serve with steamed basmati rice, and some chopped red onion with mint or coriander.