Polow (Persian Rice with Pistachios and Dill)

Using lid of pot as guide, trace circle on parchment paper and cut out. Set aside.
In large bowl, rinse rice in several changes of cold water until water runs clear. Drain well.
In pot over moderately high heat, combine 4 quarts cold water, rice, and salt. Bring to boil, then reduce heat to moderate and boil, uncovered, 5 minutes. Drain well.
In small bowl, stir together 1/4 cup warm water and saffron until dissolved.
Transfer 1 cup cooked rice to medium bowl and stir in yogurt and 1 tablespoon saffron water (reserve remaining saffron water).
In cleaned pot over moderately low heat, melt butter. Add rice–yogurt mixture, smoothing into flat layer. Top with 1/2 of remaining rice. Sprinkle with 1/2 of dill and pistachios and top with 1/2 of remaining rice, mounding loosely. Sprinkle with remaining dill and pistachios and top with remaining rice, mounding loosely into pyramid. Using round handle of wooden spoon, make 5 or 6 holes in rice to bottom of pot and pour in remaining saffron water.
Cover rice with prepared parchment paper round then with lid and steam, undisturbed, until tender and crust forms on bottom, 15 to 20 minutes.
Spoon loose rice onto platter without disturbing bottom crust. Dip bottom of pan into large bowl of cold water 30 seconds to loosen crust. Using spatula or wooden spoon, lift crust and transfer atop rice.