Bring a small pot of water to a boil. Add the potatoes and boil for 10-15 minutes.
In a medium non stick pot over a medium high heat, add the mustard seeds and allow them to pop. (About 1 minute).
Add the oil, garlic and green chilli. Saute for 1 minute.
Then add the salt, turmeric, red chilli, cumin and coriander and tomato and mix to combine. Add a splash of water.
Prick the potatoes and add them to the pan along with the tamarind paste and sugar and turn the heat down to low. Stir the mixture so that all the potatoes are coated. Add 100ml water.
Keep on low heat and cover with a lid, cook for a further 5 minutes or until the sauce has thickened slightly.