Wash 2 cups of Basmati rice till water runs clear . Pour enough water to cover the rice by 1" and set aside to soak for 30 minutes .
Preheat oven to 350 . Thinly slice the onions and set aside . Lightly spray the bottom of a cookie sheet and spread the onions in a single layer . Bake for 30 minutes till it starts to brown .
Chop the vegetables to bite size pieces . Take 1 C yogurt in a bowl and beat till smooth . Gather the spices for Biryani Masala and dry roast each (optional) in a small skillet . Powder in a blender or mortar and pestle . Set aside
Chop the ginger and garlic , along with green chili and grind to a coarse paste . Chop coriander and mint leaves and set aside . Soak the saffron strands in 1/4 C warm milk .
Drain the rice from water and set aside . Take 8 to 10 cups water in a large pot . Add the spices listed under rice along with salt and bring to boil .
While the water is coming to a boil , set a 10" skillet or a medium kadai on fire . Pour 1/4 C ghee (oil) on it . Add the cashew nuts to the hot oil and fry till brown . Drain and fry the raisins . Remove the raisins once they are puffed up and fry the dried onions till golden brown . It takes about 1 to 2 minutes .
If necessary add a couple Tablespoons more of the oil . Fry the ground paste for a couple of minutes , followed by chili powder, coriander powder and salt . To this add the ground Biryani Masala . Fry for a few seconds. Crush half of the fried onions and add to the mix as well . Stir in the blended yogurt. Add the vegetables and mix well .Cover with the lid and cook for 5 to 7 minutes over medium heat.
By now the water must be on vigorous boil . Add the drained rice to the water. Let it come back to a boil and simmer for 5 minutes .
Drain the rice in a colander . Remove any whole spice pieces that you see.
Coat the bottom of casserole dish with ghee and spread a thin layer of rice on it . Place half the vegetable mix over the rice , followed by a third of the onions , nuts and raisins and the chopped herbs . Repeat with half the remaining rice , layer of vegetables herbs and nuts . Add a final layer of rice . Drizzle the saffron milk on top, followed by a drizzle of 1 tablespoon of warm ghee. Top with raisins, cashews , and a few tablespoons of the herbs.
Cover with a foil and bake for 45 minutes . Alternately this can be layered in a thick bottomed vessel with lid . Cover with aluminum foil and top with the lid for a tight seal . Heat a thick cast iron pan on the stove top and place the vessel on top . Reduce the heat and cook for 30 to 45 minutes .