1. Wash rice well and drain in a colander for 30 mins OR drain water and spread on a dry clean piece of cloth and let dry for 30 mins
2. The rice will be more or less dry at this stage. Do not worry if it seems damp.
3. Grind it to a very fine powder (See NOTES)
4. Dry roast rice flour for a couple of mins till the grains seem separate.
5. No need to roast till it changes colour.
6. Roasting the flour makes the resulting thattai very crisp
7. Dry roast urad dal till it becomes fragrant; no need to let it turn red/brown.
8. Grind it into a fine powder once cool (See NOTES)
9. Mix all dry ingredients and rub butter into it
10. Add enough water (roughly 3/4 cup-1 cup) to make a soft pliable dough (like you`d make for rotis)
11. Preheat oven to 180 deg C OR heat oil at this stage if you plan to fry
12. Pinch out 1 tbsp-sized balls
13. Flatten on your greased palm (2-3 inch diameter) and carefully place on baking tray OR drop into hot oil and deep fry
14. Bake in the preheated oven for 15 mins. Then flip over very carefully (some may be brittle and might break) and bake for another 14-15 mins.

Notes:
1. It is difficult to powder just 2 tbsp of urad dal. So, you could powder 4-5 tbsp and use 2 tbsp in this recipe and keep rest for later
2. You can use roasted gram instead of urad dal. No need to roast these
3. We usually get the roasted rice ground at a mill. You could do this at home too. Just powder the stuff in small batches in your mixer-grinder or food processor
4. 4 cups of rice yielded around 65 unevenly sized thattais.

Recipe courtesy: foodiliciousnan