Prepare the marinade: In a mixing bowl whisk together the yogurt, garam masala, coriander, turmeric, and salt. Add the chickpeas and cauliflower and set aside.

Make the curry: Add 2 tablespoons of oil to the pan along with the onions and salt. Sauté until they are golden and lightly caramelized, about 20 minutes. Remove 1/4 of the onions (setting aside) before add the tomatoes and cook until they have broken down and turned saucy, about 5 minutes. Add the ginger, garlic, and chili. Fry for 1 minute.

Add the chickpea and cauliflower mixture, stirring to combine. Cover and cook until the cauliflower is just tender, about 10 minutes.

Layer the biryani: In a large dutch oven layer half of the curried chickpea and cauliflower mixture, followed by half of the potatoes, then about 1/3 of the reserved fried onions, then half of the rice. Repeat the layers again.

Pour the saffron and milk mixture over the top and top with the reserved fried onions.

Place a heavy lid on top and cook over low heat for 15-20 minutes to combine the flavors.