Tahchin is a celebratory dish that requires patience, but the result – a perfectly crisp, golden rice crust, called Tahdig – is worth it. The keys to success are high-quality saffron and thick yogurt.
Traditionally, only egg yolks are used for a richer color and a more stable Tahdig structure. Chicken (Morgh) is the most common filling for Tahchin, which is coated in a yogurt and saffron marinade before baking.
Place chicken, onion, turmeric, salt, and pepper in a small pot, cover with water just enough to submerge the chicken. Cook until the chicken is tender, about 30-40 minutes.
Remove the chicken, shred into large chunks or slice, and set aside. Strain the broth and reserve about 1/4 cup for the marinade.
Drain the soaked rice. Bring a large pot of heavily salted water to a rolling boil.
Cook the rice for 5-7 minutes until it is al dente (soft outside, hard in the center). Drain and rinse with cold water to stop the cooking process.
In a large bowl, mix the Greek yogurt, egg yolks, 1/4 cup of oil, and the dissolved saffron. Add a pinch of salt. Mix well.
In a small bowl, mix the shredded chicken with 3 tablespoons of the yogurt mixture and a little of the chicken broth. (Optional: Marinate the chicken for 30 minutes.)
Preheat the oven to 185 °C (365 °F).
Add the parboiled rice to the remaining yogurt mixture and gently fold it in to avoid breaking the grains and ensure the rice is evenly coated. (Divide the rice into 1/3 and 2/3.)
In a baking dish (e.g., 9x13 inches), heat the remaining 1/4 cup of oil (and some butter, if desired) in the preheated oven until sizzling. The oil should coat the bottom and sides of the dish.
Spread half of the saffron rice (or 2/3 of the mixture) onto the bottom and up the sides of the dish, pressing it down firmly.
Add the layer of marinated chicken and spread it out evenly. Cover the chicken with the remaining rice (1/3 of the mixture) and press down firmly with a spoon to smooth the surface.
Cover the baking dish tightly with aluminum foil, poking a few holes with a knife or fork (to allow steam to escape), and bake for 1 hour and 30 minutes at 185 °C (365 °F).
While the Tahchin bakes, prepare the barberries: Rinse the barberries. In a small pan, melt the butter, add the barberries and sugar. Sauté for 2-3 minutes until the barberries plump up and soften. They should not brown.
After baking, let the Tahchin cool for 10 minutes.
Place a serving platter (ideally with a rim) on top of the baking dish and quickly and carefully invert it. The Tahchin should slide out, revealing the golden, crispy crust (Tahdig).
Garnish with the barberry mixture and chopped pistachios. Serve warm.