Marinate the chicken: In a bowl, mix yogurt, lemon juice, 1 tsp garam masala, turmeric, cumin, chili powder, ginger paste, and garlic paste. Add chicken pieces and coat well. Cover and refrigerate for at least 1 hour, preferably overnight.

Cook the chicken: Heat a large pan over medium heat. Add marinated chicken and cook until lightly browned, about 5-7 minutes. Remove and set aside.

Prepare the sauce: In the same pan, melt butter. Add chopped onions and sauté until golden brown, about 5 minutes.

Add tomato puree to the onions and cook for 5 minutes, stirring occasionally. Then add remaining garam masala, sugar, and salt. Cook for another 2 minutes.

Combine chicken and sauce: Return the cooked chicken to the pan. Stir well to coat with the sauce. Simmer for 10 minutes on low heat.

Finish with cream: Pour in heavy cream and stir gently. Simmer for another 5 minutes until the sauce thickens slightly.

Garnish and serve: Sprinkle with fresh cilantro and serve hot with naan or steamed rice.