Soak the rice
Wash the rice and soak it in water for about 1 hour.
Cook the chicken
Place the chicken breast in a pot with the onion, turmeric, cinnamon, and about 2 cups of water. Cook until the chicken is tender and fully cooked.
Season the chicken
Remove the chicken and cut or shred it into small pieces. Heat a little oil in a pan and sauté the chicken with salt, pepper, turmeric, and a little cinnamon.
Parboil the rice
Bring a large pot of salted water to a boil. Add the soaked rice and cook for about 10–15 minutes. The rice should be partially cooked but still slightly firm in the center. Drain well.
Prepare the Tahchin mixture
Whisk the egg yolks in a large bowl. Add the thick yogurt, rose water, and brewed saffron. Mix well, then gently fold in the parboiled rice.
Prepare the barberries
Heat a little oil in a small pan. Add the barberries and powdered sugar and cook briefly over low heat. Be careful not to burn them.
Layer the Tahchin
Grease the bottom of a suitable pot with oil. Add a layer of the saffron rice mixture and press it gently. Add some chicken, barberries, and a few pieces of butter. Continue layering and finish with the remaining rice.
Cook the Tahchin
Cover the pot and cook over very low heat for about 30 minutes to 1 hour, until the rice is fully cooked and the bottom has developed a golden crust.
Flip and serve
Let the Tahchin rest for a few minutes. Place a large serving plate over the pot and carefully turn it over. Garnish with barberries, sliced almonds, and pistachios.
Serve
Serve the Tahchin hot with plain yogurt, fresh salad, or your favorite Persian side dishes.