01 - In a large bowl, combine chicken with yogurt, lemon juice, turmeric, cumin, garam masala, chili powder, and salt. Mix thoroughly to coat all pieces, cover, and marinate for at least 10 minutes, or up to 1 hour for deeper flavor penetration.
02 - Heat 1 tbsp butter and vegetable oil in a large skillet over medium-high heat. Add marinated chicken pieces and cook for 5-6 minutes, turning occasionally, until lightly browned but not fully cooked through. Transfer chicken to a plate, reserving any juices.
03 - Add remaining 1 tbsp butter to the same skillet. Sauté finely chopped onions for 3-4 minutes until soft and golden brown. Add minced garlic and grated ginger; cook for 1 minute until fragrant, stirring constantly to prevent burning.
04 - Stir in ground coriander, paprika, and cayenne pepper. Toast spices for 30 seconds to release their essential oils. Pour in crushed tomatoes and sugar; simmer for 5 minutes, stirring occasionally, until the mixture begins to thicken.
05 - Return seared chicken and any accumulated juices to the skillet. Simmer for 8-10 minutes over medium heat, or until chicken is cooked through and sauce has reached a rich, coating consistency.
06 - Reduce heat to low and stir in heavy cream. Simmer gently for 2 minutes to meld flavors. Adjust salt seasoning to taste. The sauce should be velvety and generously coat the chicken pieces.
07 - Transfer to a serving dish and garnish generously with chopped fresh cilantro. Serve immediately while hot, accompanied by steamed basmati rice or warm naan bread for dipping.