In a small bowl, toss the chicken pieces with Greek yogurt, turmeric, and half of the garam masala; let marinate for at least 10 minutes.
Heat the ghee in a large skillet over medium heat and sauté the diced onion until softened and translucent.
Add the minced garlic and grated ginger to the skillet, stirring for 1 minute until the mixture is fragrant.
Add the marinated chicken to the pan and cook until the edges are lightly browned.
Stir in the tomato puree, cumin, sea salt, black pepper, and the remaining garam masala.
Reduce the heat to low, cover the pan, and simmer for 10 minutes until the chicken is cooked through.
Pour in the full-fat coconut milk and stir until the sauce is smooth and heated through.
Serve the butter chicken over the warm cooked basmati rice and garnish with fresh chopped cilantro.