01 - Combine chicken with yogurt, lemon juice, turmeric, cumin, garam masala, chili powder, and salt in a large bowl. Mix thoroughly, cover, and marinate for at least 10 minutes or up to 1 hour for enhanced flavor penetration.
02 - Heat 1 tbsp butter and oil in a large skillet over medium-high heat. Add marinated chicken and cook for 5-6 minutes, turning occasionally, until lightly browned but not fully cooked through. Remove chicken and set aside, reserving juices.
03 - In the same skillet, add remaining 1 tbsp butter. Sauté onions for 3-4 minutes until soft and golden. Add garlic and ginger; cook for 1 minute until fragrant, stirring constantly to prevent burning.
04 - Stir in coriander, paprika, and cayenne. Cook for 30 seconds to bloom spices. Add crushed tomatoes and sugar; simmer for 5 minutes, stirring occasionally to allow flavors to meld.
05 - Return chicken and accumulated juices to the skillet. Simmer for 8-10 minutes, or until chicken is cooked through and sauce begins to thicken slightly.
06 - Reduce heat to low. Stir in heavy cream and simmer for 2 more minutes until sauce is velvety and heated through. Adjust salt to taste.
07 - Serve hot, garnished with chopped cilantro. Accompany with steamed basmati rice or warm naan bread.