Combine yogurt, lemon juice, garam masala, cumin, turmeric, chili powder, and salt in a large bowl. Add chicken pieces and mix until evenly coated. Cover and refrigerate for at least 30 minutes or up to 4 hours.

Heat a large skillet or heavy-bottomed pan over medium-high heat. Add marinated chicken pieces in a single layer, working in batches if necessary. Cook for 3-4 minutes per side until golden brown and just cooked through. Remove chicken and set aside.

In the same pan, reduce heat to medium and melt butter. Add diced onions and cook for 5-7 minutes, stirring occasionally, until softened and lightly golden.

Add minced garlic and grated ginger to the pan. Cook for 1-2 minutes until fragrant, stirring constantly to prevent burning.

Stir in garam masala, cumin, coriander, turmeric, and chili powder. Cook for 30 seconds until spices become aromatic and slightly darkened.

Add crushed tomatoes and tomato paste to the pan. Stir well to combine with the spice mixture. Bring to a simmer and cook for 10-12 minutes, stirring occasionally, until sauce thickens slightly.

Reduce heat to low and stir in heavy cream and sugar. Mix thoroughly until sauce becomes smooth and creamy with a beautiful orange color.

Return cooked chicken pieces to the pan along with any accumulated juices. Stir gently to coat chicken completely with sauce. Simmer for 5-7 minutes until chicken is heated through and sauce reaches desired consistency.

Taste and adjust seasoning with additional salt if needed. Garnish generously with fresh chopped cilantro.

Serve hot over fluffy basmati rice with warm naan bread on the side.