Add the salt to the water, bring it to boil and add the rice. Bring it back to boil and cook for 7 minutes. Get a grain and bite it, it should be soft on the outside and just resistant on the inside, not raw solid but almost cooked solid.
a saucepan of water, 3 Tbsp salt, 500 g Basmati rice, rinsed in cool water until the water runs clear
Drain the rice, rinse with cold tap water, drain again and set aside.
Steaming the Rice
Wash out and dry the saucepan you used to parboil the rice, then place it on medium heat.
For the tahdig, see proportions above. Mix the 2 ladles of rice, yoghurt, egg and salt in a small bowl. If not using yoghurt or egg, just move on to step 5.
2 ladles of the parboiled rice above, 1 Tbsp yoghurt, 1 small egg, ¼ tsp salt
Mix the saffron and fat of your choice and swirl it around in your saucepan for a few seconds.
1 Tbsp liquid saffron, 1 Tbsp butter
Add the rice or rice mix to the fat/saffron mix and flatten down. Leave to cook for a minute.
Gradually add the rest of the rice, ladle by ladle, forming a conical shape. The reason for this is that traditional chelow pots were conical, giving you a wide base for your tahdig. Also given the long cooking time, whatever rice that touches the saucepan is going to crisp up slightly. So you want as much of the rice away from the edges as possible.
Wrap the saucepan lid up with the towel and place on the saucepan, ensuring it's a tight fit. The towel is there to absorb any excess moisture, preventing soggy rice. Make sure your tea towel is nowhere near the flame!
Cook on that same medium heat for 5 minutes. This should be enough time for the steam to build up. My mum used to wet her fingers and touch the side of the saucepan and if it "sizzled" that meant there was enough steam.
At this stage, lower the heat right down and let the rice steam away for 45 minutes. This will produce a golden tahdig, the way I like it. If you prefer a darker shade of brown, go for 60 - 90 minutes.
At the end of the cooking time, take it off the heat, let rest for 5 minutes, then sprinkle the rose water and butter topping all over the rice, if you like, or skip this stage.
1 tsp rose water, 1 Tbsp butter
To Serve
Ladle out all that beautiful, glistening rice onto a platter, lifting out the tahdig right at the end and serving that up separately, cut or broken up into pieces.