Marinate chicken: In bowl, mix together the crushed fried onions, with all the ground spices (coriander powder, cumin powder, red chili powder, paprika), ginger-garlic paste, and yogurt. Add chicken and keep aside for 30 mins - 2 hours.
In a large pot add a cup of oil, on low heat, for 2-3 minutes. Add the whole spices: cloves, black cardamom, cinnamon stick, black peppercorn, and fry until fragrant (about 3-5 minutes).
Increase the heat to medium add the cut potatoes and cook for 3-5 minutes, until potatoes start to turn golden.
Add the marinated chicken, as well as the sauce, and ½ cup of water.
Cook on low heat for 30-45 mins, covered, until chicken is fully cooked, and oil has risen to the top.
Add korma essence or kewra essence, if using.
Garnish with cilantro
Notes
Instead of a whole chicken, you can also use 3 lbs of bone-in chicken thighs, legs and breast pieces.