To start making Onion Tomato Podi Masala, first get all the ingredients ready, including the boiled potatoes. 

We will first cook the potato masala for the Onion Tomato Podi Masala Dosa.

Next, in a small kadai heat up a tablespoon oil over medium heat. Add mustard and cumin seeds, let mustard splatter. Add curry leaves, green chili, ginger and saute for 30 seconds.

Add onion and let it cook until transparent. Add salt, turmeric powder, mashed potatoes and stir to combine.

Sprinkle some water and cook for a minute until all the ingredients are well combined. Check the salt and spices and adjust to suit your taste. Turn off the heat and keep the potato masala aside.

Heat up the dosa skillet over medium heat. Pour a ladleful of dosa batter, spread the batter in a circular motion from the inside to the out, to make a thin crepe. 

Allow the dosa to cook a little and then sprinkle chopped onion, grated tomatoes and a heaped teaspoon of Idli podi, drizzle some oil on dosa and on the sides.

Let it cook until the sides are brown. Place required amount of potato masala, fold and serve.

Serve the Onion Tomato Podi Masala Dosa immediately along with Vendakkai Vengayam Sambar Recipe (Okra in Tangy Lentil Curry) and coconut chutney.