Marination: Take 500 grams of fresh mutton pieces and place them in a large bowl. Add 100 grams of finely chopped onions, mix well with your hands, and ensure every piece of mutton is coated. Cover the bowl and set it aside for at least 30 minutes. This marination step enhances the flavor and ensures authentic Bengali-style mutton kosha with a rich taste.

Tempering Spices: Heat 3 tablespoons of mustard oil in a deep frying pan or kadhai over medium flame. Once the oil is hot, add 3 bay leaves, 1 cinnamon stick (about 2 inches), 2 dry red chilies, 6 slit green chilies, 6 cloves, 2 black cardamoms, 1 small piece of mace, and ½ teaspoon black peppercorns. Sauté the whole spices for about a minute until they release a strong aroma, creating the classic base for this spicy Indian mutton curry.

Preparing the Masala: Add 250 grams of finely chopped onions to the hot oil and sauté until they turn golden brown. Next, stir in 1 tablespoon of ginger-garlic paste and cook for another minute to remove the raw flavor. Sprinkle ½ teaspoon turmeric powder, 1 teaspoon cumin powder, 1 teaspoon coriander powder, and 1 teaspoon red chili powder. Mix thoroughly so the onions are coated with spices, giving the curry its signature deep flavor and color.

Cooking the Mutton: Add the marinated 500 grams of mutton pieces into the onion-spice masala. Stir well to coat the meat evenly with the rich masala. Cover the pan and cook on medium heat for 12–15 minutes, stirring occasionally, until the mutton starts turning tender. This slow cooking makes the Bengali kosha mutton juicy and flavorful.

Final Touch: Add 2–3 chopped green chilies to the pan and cook for another 5 minutes, allowing the mutton curry to become spicier and juicier. Once the oil begins to separate from the masala and the mutton is fully tender, garnish with fresh coriander leaves. Serve hot mutton kosha with steamed basmati rice, luchi, or parathas for an authentic Bengali meal.