Make the sauce: Place the barberries, saffron, and ¼ cup of boiling water into a small pot and set aside for 1 hour, stirring the mixture every 5 minutes. Add 1 tablespoon of oil and 1 tablespoon of sugar into the pot and place it over low heat. Cook for 10 minutes, stirring occasionally until the sugar has dissolved and the sauce is bright orange in color. Remove the pot from the heat and set it aside.

Make the rice: Place the rice in a large bowl and cover it completely with room temperature water. Soak for 30 minutes, rinse, drain and refill the water of the rice every 10 minutes until the water runs clear.

Fill a large pot with water ¾ the way up and add 1 heaping tablespoon of salt. Place the pot over high heat and bring it to a boil. Add the rice into the boiling water and cook it for 7 minutes, until it is partially cooked. Rinse and set the rice aside in a bowl.

Place 6 tablespoons of oil and ½ teaspoon of ground turmeric into the bottom of a 8 or 9-inch non-stick pot. Mix the turmeric and oil to combine. Cover the bottom of the pan with one layer of potato slices. Lightly and gently place the par cooked rice on top of the potatoes, do not mix the rice in the pot or pack it in. Using the back tip of a wooden spoon, make four evenly dispersed holes into the rice that reach the bottom of the pot (to release the steam during cooking). Place a kitchen towel over the pot, and place the lid above, tie the towel on top of the lid to keep it away from the flame. Place the pot over medium  high heat and cook the rice for about 15 minutes. Reduce the heat to low and continue cooking the rice for an additional 25 minutes. 

Remove the pot from the heat and remove the lid and towel. To turn out the tahdig, place a large flat platter on top of the pot and using a kitchen towel, hold the top of the pot with one hand and the plate with another to flip the pot and invert the tahdig onto the plate. Pour the barberri and saffron sauce over the tahdig and rice and serve immediately.