1. Prepare the Chicken: Heat 2 tbsp oil in a large pot. Brown chicken pieces on all sides, then set aside.

2. In the same pot, add remaining 1 tbsp oil. Sauté one chopped onion until translucent. Add garlic and turmeric, cook for 1 minute until fragrant.

3. Stir in tomato paste and cook for 2-3 minutes, stirring constantly. Return chicken to the pot. Add salt, pepper, and half of the saffron water. Add enough hot water to just cover the chicken. Bring to a simmer, then reduce heat, cover, and braise for 60-90 minutes, or until chicken is tender.

4. Prepare the Rice: Rinse basmati rice several times until water runs clear. Soak in salted water for at least 30 minutes.

5. Bring a large pot of salted water to a rolling boil. Drain the soaked rice and add to boiling water. Cook for 7-10 minutes, until rice is al dente (still firm in the center but soft outside). Drain in a colander.

6. Assemble the Rice: In a clean large non-stick pot, melt 2 tbsp butter with 1 tbsp oil. Layer a thin amount of rice on the bottom to create a tahdig layer. Gently spoon the remaining rice into the pot, mounding it into a pyramid shape. Drizzle remaining saffron water over the rice.

7. Cover the pot with a clean kitchen towel (or paper towel) under the lid to absorb steam. Cook on medium-high heat for 5-10 minutes (to set tahdig), then reduce heat to low and cook for another 40-50 minutes, or until rice is fluffy and tahdig is golden.

8. Prepare the Barberries: While rice cooks, rinse barberries thoroughly and drain. In a small pan, melt 2 tbsp butter. Add barberries, sugar, and a pinch of saffron. Sauté gently for 2-3 minutes until barberries are plump and glossy. Be careful not to burn them.

9. Serve: Once chicken and rice are ready, gently fluff the rice. Carefully remove the tahdig from the bottom. Mix a portion of the white rice with some of the prepared barberries. Serve the braised chicken alongside the saffron and barberry rice. Garnish with pistachios if desired.