Peel, wash and grind ginger and garlic into a fine paste.
Soak the washed rice for half an hour.
Boil 4 cups of water in avessel,add bay leaves,cloves the cardamoms, cinnamon, mace and 1 tsp of salt.When the water starts boiling,add rice.
Cook for 8-10 mins, stirring frequently or till rice is 3/4th done.Drain in a colander.
Heat oil in a non stick pan,add onions,stir fry on high heat till onions turn translucent.Add ginger garlic paste and cook briefly.
Add chilli pwdr, coriander pwdr, crushed peppercorns, cumin pwdr and turmeric pwdr.Stir fry a little and add pureed tomatoes.
Continue cooking over high heat till masala is fairly thick.Add yogurt, garam masala pwdr and half the quantity of chopped coriander and mint leaves.Stir well and cook for 2 mins more.
Add mushrooms and salt to taste and stir fry on high heat for 2 mins and remove from heat.
Arrange the cooked rice and mushroom masala in alternate layers in a biryani handi or an oven proof dish, sprinkling the chopped coriander and mint leaves ,the kewra water and the milk with saffron.Ensure that the topmost layer is of rice.
Cover the assembled Biryani with a tight lid and seal the edges with kneaded Atta (wheat flour) dough.
Keep the dish on a tawa or iron griddle and cook on low heat for 10 – 15 mins.Alternatively cook in a pre heated oven at 160 deg C for 10- 15 mins.
Break open the seal and serve Biryani immediately with a raita of your choice.