In a non-reactive bowl, whisk together yogurt, 1 tbsp ginger-garlic paste, garam masala, turmeric, chili powder, lemon juice, and salt.
Fold the chicken cubes into the marinade, ensuring even coating, and refrigerate for a minimum of 30 minutes.
Heat 1 tbsp of ghee in a heavy-bottomed pan over high heat; sear chicken pieces in batches until deeply browned and slightly charred, then set aside.
In the same pan, add remaining ghee and toast cumin seeds for 30 seconds until fragrant.
Add diced onions and sauté until translucent and golden brown, approximately 8 minutes.
Incorporate the remaining ginger-garlic paste, coriander, and paprika, cooking for 2 minutes to release essential oils.
Deglaze the pan with tomato passata and sugar, then simmer over medium-low heat for 15 minutes until the sauce thickens.
Stir in the heavy cream and return the seared chicken to the pan; simmer for 10 minutes until the chicken internal temperature reaches 74°C.
Mount the sauce with cold butter cubes for a glossy finish and garnish with chopped cilantro before serving.