In a large bowl, combine yogurt, garam masala, turmeric, cumin, paprika, and salt. Add chicken pieces, ensuring they are well coated. Cover and refrigerate for at least 1 hour to tenderize and infuse flavors.

Heat a tablespoon of oil in a large skillet over medium heat. Add marinated chicken and cook until browned and cooked through, about 8-10 minutes. Remove and set aside.

In the same skillet, melt butter and add chopped onion. Sauté until translucent, about 5 minutes. Add garlic and ginger, cooking for another minute. Stir in tomato puree and cook for 10 minutes, stirring occasionally, until thickened.

Return cooked chicken to the sauce, stirring well. Pour in heavy cream, simmer gently for 10 minutes to meld flavors, adjusting seasoning as needed. Garnish with cilantro if desired.