Heat the oil. Fry the whole red chilli, mustard seeds and curry leaves until seeds start to pop
Add the peeled tomatoes, tomato puree, salt, turmeric, sugar and chilli powder. Stir well and cook until well blended
To thicken the gravy, dissolve the gram flour in cold water and add to the above mixture. Stir until it has mixed well with all the spices
Add boiled gram (or chick peas), tamarind water and potatoes and cook for a few minutes
Add hot water depending on the thickness of the gravy required
If raw mango is available, cut and add to the above and cook for a few minutes
Otherwise add lemon juice and remove from heat
Serve with tamarind chutney, chevdo, potato or cassava crisps