Marinate mutton in yogurt,ginger garlic paste and biryani masala.. leave for an hour
Heat oil and fry onion until they become golden,then take out 2 tbsp of onion and keep aside.in the same oil with onion add mutton and fry well for 5 to 7 minutes, cover and cook on low heat until meat becomes tender... remove when one cup of stock remains

For rice
In a separate pan add water,2tbsp salt and boil.then add soaked rice, when more than half rice is cooked, remove from heat and stain water...

Assembling
Spread prepared masala on rice in two layers and also spread some mint,coriander leaves and green chillies and on top spread the brown onion.. cover and cook on low heat for 10 to 15 minutes, when rice is done,mix and serve....