Add saffron threads to one cup of very warm water and let bloom for at least 10 minutes. Zest the rind of one orange.
It's important to rinse the rice well. You can rinse in a strainer under cold water (hope your'e on dock water for that!) Or swish it around in a pan and rinse several times until the water runs clear.
In a large pot, cook your rice in 4 cups of salted water (1-2 tablespoons salt) until JUST al dente, about 6-8 minutes. You should see steam holes starting to appear. Remove from heat.
Take one cup of the cooked rice and place in a medium sized bowl. Stir to cool down slightly. Add the yogurt, oil, and 2 tbsp of the saffron water and mix thoroughly.
Spread the rice-yogurt mixture evenly on the bottom of a 10-inch nonstick pot with a tight fitting lid.
Sprinkle 1 cup of the remaining cooked rice on top, followed by 2 tablespoons of the currants, a pinch of orange zest, and a pinch of cinnamon.
Continue layering like this until the rice is all used. Pour the remaining saffron water on top and dot generously with butter. Wrap the lid with a dish towel and place on top. This helps absorb the moisture which you want for the crisp bottom.
Place on low heat and simmer for 30 minutes. You can peek occasional to see if the edges of the rice are getting brown and crispy. Don't remove from the heat until you see that. You may need to lift the rice up a bit with a small spatula to check. Remove from heat and lift off the cover.
Place a round serving platter (larger than your pan!) over the pan. Then gently flip! Lift off the pan and your Tahdig will be ready for serving!
Sprinkle the top with chopped pistachios, more orange rind and currants. Serve up with a spatula or large spoon.