In a bowl, combine the cleaned prawns with the yogurt, lemon juice, turmeric powder, 1/2 teaspoon of Kashmiri red chili powder, 1/2 teaspoon of salt, and 1/2 tablespoon of ginger-garlic paste. Stir until well coated. Cover and set aside in the refrigerator to marinate for 20 minutes.

Heat 3 tablespoons of oil or ghee in your heavy-bottomed pot over medium heat. Add the sliced onions and fry for 12 to 15 minutes, stirring frequently. The onions should turn golden brown and crisp. Remove half of the fried onions using a slotted spoon and drain them on paper towels; reserve these for layering later.

While the onions are frying, bring 6 cups of water to a boil in a large pot. Add 1 tablespoon of salt, the bay leaf, crushed green cardamoms, cloves, and cinnamon stick. Add the soaked and drained basmati rice. Cook over medium-high heat for 7 to 8 minutes. Test the rice: it should be cooked on the outside but still have a firm bite in the center. Drain immediately in a colander and set aside.

In the heavy-bottomed pot containing the remaining fried onions and oil, lower the heat to medium-low. Add 1 tablespoon of ginger-garlic paste and the slit green chilies. Sauté for 2 minutes until the raw smell disappears. Stir in the remaining 1/2 teaspoon of Kashmiri red chili powder, coriander powder, cumin powder, and garam masala powder. Cook for 1 minute, stirring constantly.

Increase the heat to medium. Add the marinated prawns along with all of the marinade liquid to the spice base. Stir well and cook for 4 to 5 minutes, just until the prawns turn pink and start to curl slightly. Do not cook them fully. Turn off the heat.

Spread half of the chopped mint and coriander leaves over the prawn mixture in the pot. Layer all of the parboiled rice evenly over the top. Scatter the reserved fried onions and the remaining mint and coriander leaves over the rice. Drizzle the saffron milk (if using) and 1 tablespoon of melted ghee over the surface.

Cover the pot with a tight lid. To seal the steam, you can place a piece of aluminum foil under the lid before closing. Cook on the lowest heat setting for 15 minutes. Turn off the heat and let the pot sit, unopened, for 5 minutes. Remove the lid and gently fluff the biryani with a fork, mixing the layers slightly before serving.