Put a little clarified butter/ghee in a pan, heat it and fry onion rings in it till they turn brown.
Make a paste by grinding a small portion of the browned onions, ginger, garlic, mace, nutmeg, green chillies, coriander mint leaves, poppy seeds, tomatoes, chopped onions and half of the cinnamon, cloves, black green cardamoms, black peppercorns and bay leaves.
Next, take the chicken pieces and make some cuts on them.
Take a bowl and put in it the yoghurt, red chilli powder, garam masala powder, turmeric powder and the ground paste with some salt.
Mix well and rub this mixture on the chicken pieces.
The paste needs to enter the chicken pieces.
So leave it for at least an hour.
Combine the rice, water, milk, remaining whole spices (except cumin seeds) and salt in a large vessel.
Cook this till the rice is half done.
When that's done, drain away the excess liquid and then spread the rice on a plate to cool.
Put the clarified butter/ghee in a heavy bottomed pan, heat it and when it is hot, splutter some cumin seeds.
Then add the chicken pieces with the marinade and cook on a high flame.
Do this for a few seconds.
Now, take the fried potato halves.
Add them to the chicken pieces and mix well.
Cover it and cook on a low flame for 15 mins, or cook till the chicken is almost done.
Remove from flame and keep aside.
Next, arrange the rice and the chicken in layers.
To begin with, put the ghee/butter in the same heavy bottomed vessel and arrange a layer of chicken with gravy, a layer of rice topped with a portion of brown onions and saffron milk.
Repeat the same process, till all is used up.
Keep the topmost layer of rice with melted clarified butter (ghee)/butter, browned onions and saffron milk on top of it.
Once the arrangement of the ingredients in layers is concluded, spread an aluminum foil on top of the pan and use a tight fitting lid to cover it.
Cook over a very low flame for the next 12 mins, placing the biryani on a tawa.
For garnishing, use fried cashew nuts and raisins.