Cut chicken into bite size pieces. Toss with ginger paste, garlic paste, chile powder, dhana-jeera powder and black pepper. Leave to marinate for 15 minutes.
Heat milk. Add saffron and let stand for 15 minutes.
Place barberries in a bowl and cover with boiling water for 15 minutes. Drain and set aside.
In a large pot, heat oil. Add whole spices and fry for 1 minute.
Add onion and chiles and fry for 10 minutes, stirring often, until caramelized.
Remove onions and spices from pot.
Add chicken and fry until browned.
Return the onion and spices to the pot.
Add barberries, sugar, salt, saffron milk, rice and 3 cups water. Bring to a boil.
Reduce to a simmer, cover and cook for 15 minutes.
Fluff with a fork and serve, garnished with pistacchios.