Sieve rice flour and urad dhal powder. Add soaked Bengal gram dhal, chilli powder, asafetida, butter and salt to the flour. Mix well. Add water little by little and make a dough. Take little dough and put it in a greased plastic sheet. Pat it and make it thin and round. Prick it a fork in two or three places, so that when it is fried, it will not raise like puri and it will be flat.
Heat oil in a kadai. When it is hot, put four or five round thattai and fry till it become golden brown and crisp. Store it in an airtight container.
Note: If you like garlic taste, then instead of red chilli powder, you can grind 3 to 4 red chillies along with five to six garlic flakes and add it to the flour while mixing.
If you are making in bulk quantity, you can mix raw rice, pottukadalai, urad dhal (Fry slightly) and send it to Flour Mill for grinding. In such case for 1 cup rice, add half cup Pottukadalai and 1 tablespoon fried Urad dhal.