Heat ghee on medium-low. Add whole spices; let them bloom 30 sec.
Add the white onion paste. Cook 8–10 min, stirring constantly — do not let it brown. It should stay pale ivory.
Add cashew-poppy paste. Cook 3–4 min until the ghee separates at the edges.
Lower the heat. Add marinated chicken. Stir gently to coat.
Cover and cook 20 min on low, stirring every 5 min. The chicken releases its own moisture — resist adding water.
Add warm milk, sugar, green chilies, and salt. Simmer uncovered 8–10 min until chicken is tender and gravy is silky.
Finish with kewra water. Rest 5 min off the heat.