You have made it in Persian cooking if you make a good Tah-dig, the perfect crusted rice that stays together when dumped sand castle style on your platter. The crunch of the crust with the soft tender rice is sublime.
Another great food introduced to us by my brother-in-law from Iran.
Put sugar cube in a small mortar add the saffron threads to the top of it. Using the pestle, crush together into as fine a powder as possible. Place in a small cup. Add melted butter and boiling water. Set aside for 3 hours.
Soak washed rice in lukewarm water that generously covers it for 30 minutes. Drain
Put 10 cups water into a large pot and bring to a boil. Add 1 1/2 tablespoons salt and mix in. Scatter rice into the boiling water and bring to a boil again. Boil rapidly for 5 1/2 minutes. Drain rice immediately and leave in colander.
Put the butter in a nonstick pan and set over low heat. Add 2 tablespoons water plus 2 teaspoons of the saffron mix. Peel potato and cut into 1/8" slices.
Lay slices in an even layer in the bottom of the pan. Cut slices to fit to completely cover bottom if desired. A few blank spaces are fine.
When the butter is melted dump the rice on top of the potato slices. Cover and turn to medium-high. After 4 minutes, add the remainder of the saffron by dribbling over rice. Do this quickly
Drape a dish towel over the underside of the lid and then place back on the pan. (The towel will between the pan and the lid) Flip the towel ends on top of the lid so they do not burn. Turn heat to lowest heat possible and cook for an additional 25 minutes.
To serve, have a large warm serving plate ready. Remove cover and slide a knife along the inside of the pan to loosen rice. Put the serving plate on top o the pan of rice. Now, turn it over to invert rice on to the plate.
The "cake" will crumble a little, spreading out at the bottom, but this is as it should be. Serve immediately, cut into crust to serve.
Alternatively, empty just the rice rice onto the serving plate, scooping our gently with a spoon. Now remove the crust from the pan and with a butter knife or pair of kitchen scissors, cut into even wedges. You may arrange the wedges, crusty side up, around the rice or serve them on a separate plate.