It adds a lovely citrus zing to this rich curry and can be substituted with ... Add the chilli powder, turmeric, coriander, cumin and garam masala. Stir in the tomato purèe.
About 30 minutes before serving, stir in the garam masala and yoghurt ... Alternatively, you can cook this curry on the hob for 2-3 hours on a low heat, or until the beef is very tender.