You can use Idli steamer or pressure cooker to steam cook the flour. I used pressure cooker and steamed for about 15 minutes without keeping the whistle.
If you are making in large quantity, you have to extend steam cooking for few more minutes.
Do not try to break the flour immediately after steam cooking and let it cool down for 5 minutes.
I usually press the murukku over a square paper, so that I can easily slide them in to oil without altering the shape of chakli.
You can use either black or white sesame seeds. But roast them before use.
To check oil, drop a pinch of dough and see if it raises to the surface immediately. If so, the oil is rightly heated and you can start deep frying.
Always keep the flame medium low when you are deep frying.