Take flour and salt in a bowl, mix. Add mashed potatoes.
Mix well by rubbing between your finger and thumb. If you pinch a small portion together it should form like a dry dough.
Depending on how much moisture is present in your boiled potato, you may or may not need any extra water. If yours look dry then add 1 teaspoon of water at a time and knead into a soft, smooth dough. Be careful while adding water. If you add all at once, it becomes sticky and pasty, we do not want that. Cover and let it rest for 10-15 minutes.
Rolling & Frying Poori:
Divide the dough into 10 equal portions and make smooth round balls. Work with one ball at a time.
To avoid sticking to the surface, use a ziplock bag or parchment paper. Place one ball on it, cover with another piece of ziplock or paper and pat it with your fingers and make a round shape and keep the medium thickness. You can use a rolling pin but be very gentle.
If the edges are breaking then seal it and pat it again to get even thickness. Prepare 4-5 pooris and keep it covered in a plate.
Now heat the oil in a pan for frying on medium-high heat. Oil should be hot (not medium). Once hot add one poori at a time. It will puff up. Once browned from the bottom side then flip it and cook another side.
Drain the excess oil using a slotted spatula, remove it to the paper towel lined plate and fry rest of them.
Water amount: Depending on your boiled potato’s moisture content, you may or may not need any water. Do not use over-boiled potato which as too much moisture and can result in sticky dough.
If water is needed then add very little water (about ½ to 1 teaspoon) at a time and knead. If you dump all the water at once, the dough will be sticky and pasty. If by mistake this happens then add little more rajgira atta and knead.
Roll or pat the puri at medium thickness, meaning not too thick not too thin. If it is thick then it will sink into the oil, will take more time to cook and may not puff up. If it is thin then it may break, soak up too much oil and will not puff.
Use the Ziplock bag or parchment paper while rolling the puri. Otherwise, it will stick to the surface.
Fry the pooris into HOT oil. If oil is not hot enough, then it will absorb too much oil and will not puff well.