Preheat oven to 375 deg F. Spread the potato-cauliflower mixture on one or two sheet pans. Add 2 tablespoons of oil to each pan of vegetables.Season lightly with salt. Mix well and roast in the oven for 40-45 min or until golden brown and fully cooked. Remove from heat and keep aside.
Once the vegetables are in the oven, wash and rinse the rice couple of times. Soak in clean water for 15 minutes. Once the 15 minutes are up,drain and keep aside.
When the veggies in the oven are half way through, heat 2 tablespoon of oil or ghee at "medium low" level in a large deep pan. Now add all of the whole spices. Saute regularly while letting the spices toast in the oil for 2 minutes.
Now add the onions and saute for 3-4 minutes. Add the ginger garlic paste. Cook for 5 minutes until you can no longer smell the raw paste.Add the chopped tomatoes. Mix and cook for a couple of minutes.
Add the powdered turmeric, cumin, coriander and chilli powder. Mix and cook for a minute.Season with some salt. Add 2 cups of hot water to this mixture. Mix well and let this mixture cook down for 5-6 minutes until the onion-tomato mixture has fully softened.
Now add the whisked yoghurt and mix. Add half of the chopped cilantro and all of the chopped mint leaves. Saute well and add around ¾ of the cooked potato-cauliflower mixture. Add the garam masala and mix.
Add the rice and 4 cups of water. Season with more salt. Stir the contents of the pot well and cover with a lid. Ensure the heat is maintained at "medium" to bring the water to a boil.
After 12 minutes, stir all the contents and see if the rice is done. If it still needs more water, add around ½ cup of water and cover the lid again. Check after 5 minutes. Turn off the heat once the rice is completely cooked.
Top with the remaining roasted vegetables and chopped cilantro,mint leaves. Serve hot with raita or any other dish of your choice.