Heat 5-6 tbsp oil in a pressure cooker or heavy bottom pan and add the whole spices.
Give a stir and when it splutters, add the 5 medium sized sliced onions.
Fry on high heat for around 12 mins till the onions are light brown.
Now add the marinated mutton, mix and fry on high heat for 3 mins.
Now continue to fry the mutton on medium heat for another 5 mins till oil separates. (Readymade Biryani Masala usually contains salt, hence salt is not added while cooking the mutton in this recipe. Do check if the biryani masala you are using has salt in it or else add as per your taste.)
Add 150 ml water, give a mix and close the pressure cooker. In case the pressure cooker has a whistle cook for 3 whistles ( on high heat till 1st whistle and on low for next 2) or for 15 mins when using a different kind of pressure cooker.
In case you’re not using a pressure cooker, continue to cook covered on low heat for 45-60 mins till meat is tender and add water as & when required. Give a stir few times so that it doesn’t get stuck at the bottom.
Once the pressure has released, open the lid & dry up any excess water to get a thick gravy.