Mash the boiled potatoes corsely and keep them aside.Sprinkle a little salt and mix them gently.This way the salt will be soaked by the potatoes and when cooked in the curry they will not taste bland.
Chop the tomatoes finely.Chop the ginger and green chillies.
Heat oil/ghee in the pan.Add the cumin seeds and let them splutter. Now add the chopped ginger and green chillies. Saute them for few seconds and add the chopped tomatoes.
Add the salt and red chili powder (optional) and turmeric powder. The red chilli powder and turmeric powder is optional.
Cook covers till oil separates.
Now, add the potatoes and mix well. Cover again and cook for 5 minutes. Add a little water if it sticks at the bottom. After 5 minutes add 1/2 cup water ( approx) to make curry and bring to one boil. Mix well.