In a medium bowl, combine the chicken pieces with the yogurt, turmeric powder, and a pinch of salt. Mix well and let it marinate for at least 30 minutes (or up to 2 hours in the refrigerator).

Heat the ghee or oil in a large, heavy-bottomed pot or Dutch oven over medium heat. Add the chopped onions and sauté until golden brown, about 8-10 minutes. Be patient, as this step builds a crucial layer of flavor.

Add the minced garlic, grated ginger, and slit green chilies (if using). Sauté for another minute until fragrant, being careful not to burn the garlic.

Stir in the ground cumin, ground coriander, red chili powder, and garam masala. Cook for about 30 seconds, stirring constantly, until the spices are fragrant.

Pour in the crushed tomatoes and cook, stirring occasionally, for about 5 minutes, allowing the tomatoes to break down and meld with the spices.

Add the marinated chicken pieces to the pot. Increase the heat slightly and sear the chicken for a few minutes on each side until lightly browned.

Pour in the water or chicken broth, scraping up any browned bits from the bottom of the pot. Bring the mixture to a simmer, then reduce the heat to low, cover, and cook for 20-25 minutes, or until the chicken is cooked through and tender.

Stir in the heavy cream (if using) and season with salt to taste. Simmer gently for another 2-3 minutes until the sauce has thickened slightly. Do not boil after adding cream.

Garnish generously with fresh chopped cilantro before serving.