Pressure cook potatoes with water until soft. Cool it, peel off the skin and mash it up roughly. Keep aside.Take little and mash it up well.
Heat oil in a pan, add mustard seeds, urad dal allow it to crackle then add curry leaves,ginger and green chillies fry for a minute.
Then add onion saute till slightly browned.
Then add tomato and saute till tomatoes raw smell leaves.
Add mashed potatoes along with turmeric powder.Mix well.
Add 1 cup water, required salt and allow it to boil.
While cooking,mash with the laddle.
Allow it to get nicely blended when it all comes together as a mass to a semi thick consistency,switch off.
Your potato masala is ready now. You can pair with pooris or use the masal for masala dosai. Enjoy Poori Masala!