In a dry non stick pan over a high heat, add the mustard seeds and when they begin to pop pour in the oil.
Turn the heat down and add the curry leaves and garlic cloves, stirring continuously for 1 minute.
Stir in the blended tomatoes, red chilli powder, turmeric and salt. Allow to cook out for 3 - 4 minutes.
Mix in the tamarind and ketchup and allow to cook for 2 minutes.
Stir in the chickpeas with half a coup of water and potatoes and allow to simmer for 10 - 15 minutes.