Marination: In a large bowl, combine the mutton pieces with ginger-garlic paste, yogurt, biryani masala powder, salt, and half of the chopped mint and cilantro leaves. Mix well, ensuring that each mutton piece is coated evenly. Cover the bowl with plastic wrap and refrigerate for at least 2 hours, preferably overnight, for the flavors to penetrate the meat.

Rice Preparation: Rinse the basmati rice under cold water until the water runs clear. This step removes excess starch and prevents the rice from becoming sticky. Soak the rice in water for 30 minutes, and then drain.

Cooking the Rice: In a large pot, bring water to a rolling boil. Add whole spices (green cardamom, black cardamom, cloves, cinnamon, bay leaves, cumin seeds, and black peppercorns), salt, and the drained rice. Cook the rice until it is 70-80% done (slightly firm to the bite). Drain the rice and set it aside.

Add the chopped tomatoes, slit green chilies, and the remaining chopped mint and cilantro leaves to the mutton mixture. Mix well and cook on medium heat for another 15-20 minutes, or until the mutton is almost cooked.

Layering and Cooking the Biryani: Lower the heat to a simmer. Layer the partially cooked rice over the mutton mixture in the pan, spreading it evenly. Drizzle the saffron-infused milk and the reserved fried onions over the rice. Cover the pan with a tight-fitting lid or aluminum foil, sealing the edges to trap the steam inside. Cook on low heat for 25-30 minutes, allowing the rice and mutton to fully cook and the flavors to meld together.

Once cooked, gently fluff the rice with a fork to mix the layers, being careful not to break the rice grains. Your Mutton Biryani is now ready to serve.