Add mashed potatoes. Mix well using your fingertips.
Now add warm water little at a time and start kneading the dough. The dough should be medium soft. Cover and let it rest for 15 minutes.
Rolling & Frying Poori:
After the resting time, knead a couple of times to smooth out. Then divide into 7 equal portions. Make smooth balls and flatten between your palm.
Take one flattened disc, and roll into about 3 inches diameter circle.
Now heat the oil in a pan on medium heat. While the oil is heating, roll a few puris and keep them on a plate. Once the oil is hot, slice one rolled puri carefully. Slightly press in a circular motion using a spatula, so it will puff up.
Once puffed, flip the puri and cook another side. Then remove it to a paper towel lined plate and repeat the same for rest.
Notes
The color of the poori: Some buckwheat flour is darker in color while some is lighter. So what type and brand you are using, the color may vary.
Mash the potatoes very well. If there are tiny pieces of potato in the puri, it will not puff well.
Thickness of the puri: Roll the puri to even thickness. If it is uneven then it will not puff up while frying. Also, keep the medium thickness (not too thin or not too thick)
Fry the puris into hot oil. If oil is not hot then puri will absorb too much oil because of the potato in it. Also, it may not puff up.
How to check oil is for frying? If you drop a tiny portion of dough, it comes on top steadily meaning oil is perfect for frying. If comes on top immediately then it is too hot. If it stays at the bottom for some time and comes on top very slowly meaning it is not hot enough.
Because kuttu generates the warmth in your body, it is advisable to serve with yogurt-based dishes.