Filter the flour in a utensil through a strainer and keep it aside. Now add grated potatoes ,salt and ajjwain to flour and mix. With the help of water knead a hard dough.
Make round balls(similar to a small lemon) of the dough and flatten them with a rolling pin. The puris should be 3-4 inches in diameter.
Heat oil in a pan(kadhai). When oil is well heated put puri in it. Use a ladle to press puri which in turn makes them puffy. When puri is puffed, turn it over. Once both sides turn brown take it out from the pan.Place puri on a plate covered with a napkin, repeat the process with all the other puris .
Serve hot Aloo puris with your favourite chutney and savour the taste.