In a large bowl add the chicken, yogurt, ginger-garlic paste, chilli powder, turmeric powder and salt and marinate for at least 1 hour or over night is better.
Heat 1 tbsp of oil/ghee in a large thick bottomed on medium heat and fry the potatoes until golden brown. Drain and remove from the oil and keep it aside.
In the same pan add another 2-3 tbsp of oil or ghee. Add the bay leaves and sliced onions and fry until soft and light brown in colour.
Now slowly add the chicken along with the marinade and fry the chicken along with the onions on medium-high heat for 12-15 minutes.
Now add the potatoes, 2 tbsp of biryani masala along with 1 cup of warm milk and 1/2 cup of water and mix everything well. Cover and cook the chicken and potatoes on medium -low heat stirring frequently for 20-30 minutes.
Cook the chicken and potatoes until it's almost done. And you see the oil floating on top. The chicken curry is supposed to be on the drier side, so if its too watery you can simply rank up the heat and cook until you get the desired consistency.
Finally add kewra water and mix well. Take it off the heat, cover and keep it aside for layering.