Use the same batter for iddli ( https://calinskitchen.com/2014/10/10/iddlis-south-indian-food/),and add a little water for dosai.Smear  dosai pan.Pour a ladle of the batter and spread thinly.Pour a tsp.of butter/ghee or oil.(for crispy dosai).Keep 2 -3 tblsp.of the filling and roll or fold into cones or triangles and serve.Now for the authentic potato filling.This same filling is a good accompaniment for pooris,and is a delight in south Indian cuisine.

For  the potato masala

Ingredients

4-5 potatoes

1/4 cup green peas(optional)

2 onions chopped

3-4 green chillies(sliced)

a small piece of ginger chopped

1/2 tsp whole peppercorns

1 tblsp urad dhal or gram dal for tempering

1/2 tsp.mustard seeds

2-3 dry chillies

a pinch of asafoetida

1/4 tsp turmeric

curry leaves

1 tblsp.wheat flour/gram flour mixed with 1/4 cup water

coriander leaves for garnishing

1 tblsp.ghee/oil

Boil and peel the skin off the potatoes and mash coarsely.Heat oil.Add asafoetida,then mustard seeds.When the seeds splutter add dal,curry leaves,dry chillies.Next add the onions with the peppercorns,green chillies ginger. Saute till onion is pink not brown.Then add the boiled potatoes with turmeric and mix well for 2-3 minutes.Lastly add the flour mixed water and cook for 1 minute.Remove from fire.Garnish with coriander leaves.

There are many types of fillings for masala dosai,other than the potato filling like mixed masala vegetable filling(with beetroot,carrot,drumstick,potato,paneer filling),which i will be posting later with non vegetarian fillings too.