In a wide bowl, measure the flour. Add the mashed potato, cumin seeds and salt and mix it well.
The flour would be having enough moisture from the potato to bind it together. Just add water little by little and make a tight dough. Make sure to not add too much water as the dough will become sticky.
Add a teaspoon of oil and knead the dough once again. Cover the dough and let it rest for 20 to 30 minutes.
In the meantime, heat oil in a pan to deep fry the pooris.
Pinch small balls out of the dough.
The pooris would be hard to roll as the rajgira aata / amaranth flour does not have any gluten. Hence, we either pat it with hand to shape the poori or roll it between plastic sheet. I rolled the poori between plastic sheets (I used Ziplock bags). Tear the bag in the edge and grease the two sides of the bag.
Place a ball of dough between the two sheets and using a rolling pin gently roll the dough into a circle.
Deep fry the rolled poori in hot oil until golden brown on both the sides. Make sure the oil is hot when you deep fry the pooris or else it will absorb too much oil.
Drain the poori on a paper towel and serve warm with subzi. I served it with Potato Masala.