Soak the saffron in the warm milk. Drain and boil rice in four cups of boiling salted water with green cardamoms, black cardamom, cloves, cinnamon and bay leaf, until three-fourths done. Drain excess water. Heat oil in a kadai and deep-fry the onions till golden. Drain on absorbent paper.
Blanch all the vegetables separately. Drain and refresh in cold water. In a bowl, mix the vegetables with the yogurt, ginger-garlic paste, green chillies, coriander powder, turmeric powder, chilli powder, half the garam masala powder, salt and half the browned onions.
Transfer the mixture to a pressure cooker. Spread the rice over the vegetables. Sprinkle the saffron-flavoured milk, coriander leaves, mint leaves, kewra essence, ginger strips, remaining garam masala powder and remaining browned onions over the rice.
Seal the cooker with the lid and cook over medium heat, without the weight, till the rice and vegetables are done. This may take around fifteen to twenty minutes. Serve hot with a raita of your choice.