Crush saffron and steep in hot water to create a saffron infusion.

Sauté sliced onion and crushed garlic in oil.

Add chicken breasts to the pan, season with salt and pepper, and add water.

Cover and cook chicken until done.

Combine Greek yogurt, saffron infusion, salt, pepper, and egg yolks.

Mix until yolks are broken and ingredients are combined.

Break cooked chicken into medium chunks and fold into the saffron yogurt mixture.

Cover and chill for at least 12 hours or overnight.

Rinse basmati rice until the water runs clear; optionally soak overnight.

Preheat oven to 350°F (175°C) and grease a casserole dish.

Boil water with salt in a heavy-bottomed pot.

Add rice to the boiling water and cook until al dente.

Drain rice in a colander.

Prepare barberries by rinsing them in cold water and soaking for 10 minutes.

Warm oil in a pan and add barberries, sugar, and remaining saffron infusion.

Cook until sugar dissolves and barberries plump up.

Remove chicken from the saffron yogurt mixture.

Fold the cooked rice into the yogurt mixture, seasoning with salt as needed.

Add half of the rice mixture to the greased casserole dish.

Arrange chicken pieces atop the rice, sprinkling with the barberry mixture.

Add the remaining rice mixture, pressing down lightly to create an even layer.

Drizzle with melted butter and cover with tin foil.

Bake for 2 hours at 350°F (175°C).

Invert the cooked rice onto a serving dish.

Top with extra barberry mixture, dried rose petals, and pistachios, if desired.

Cut into square slices and serve.