Pressure Cook sweet potato for 1 whistle, put a pan on the stove, pour oil, once the oil heats keep mustard and cumin seeds, once it starts spluttering add onions, curry leaves, green chilli. Roast it, add ginger garlic paste, salt and turmeric. Add boiled sweet potato and close it with a lid and keep the stove in low flame.After few seconds add chilli powder, coriander powder, cumin powder. After few seconds add tamarind juice and keep the stove in medium flame. Boil it well.