Heat mustard oil until slightly smoking. Lower heat. Add bay leaves, cumin, cardamom, cloves, and cinnamon. Sauté briefly until fragrant.
Add sliced onions. Fry on medium heat until golden brown (10–12 min). Add ginger and garlic. Sauté until raw smell disappears.
Add tomatoes. Cook until they break down and oil separates. Add turmeric, red chili, and coriander powder. Fry until it forms a thick paste.
Add mutton and coat well in the masala. Cook uncovered for 10–15 min, stirring occasionally.
Add 1½ cups warm water. Simmer covered on low for 45–60 min or pressure cook for 3–4 whistles on medium heat.
Add garam masala. Simmer uncovered for 5–10 min. If curry tastes bitter, adjust with butter, cream, or tomato.
Garnish with coriander. Serve with rice, pulao, roti, or paratha.