Marinate the Chicken: In a large bowl, combine the chicken pieces with all the marinade ingredients: yogurt, lemon juice, garam masala, turmeric, Kashmiri chili powder, cumin, ginger, garlic, and salt. Mix well until the chicken is fully coated. Cover and refrigerate for at least 1 hour, or up to 8 hours for the best flavor.

Cook the Chicken: Heat a large skillet or Dutch oven over medium-high heat. Cook the chicken in batches, searing each side until golden brown and cooked through. Set the cooked chicken aside on a plate. You don't need to clean the pan.

Start the Sauce: Reduce the heat to medium. Add the ghee or oil to the same skillet. Add the chopped onion and cook until softened and translucent, about 5-7 minutes. Add the ginger and garlic and cook for another minute until fragrant.

Bloom the Spices: Stir in the ground coriander, cumin, and garam masala. Cook for about 30 seconds, stirring constantly, until the spices are aromatic. This step is key to developing a deep flavor.

Simmer the Sauce: Pour in the crushed tomatoes, scraping up any browned bits from the bottom of the pan. Bring to a simmer and cook for 5 minutes. Stir in the full-fat coconut milk and optional sugar. Let it simmer gently for 10-15 minutes to allow the flavors to meld and the sauce to thicken slightly.

Combine and Finish: Return the cooked chicken to the skillet with the sauce. Stir to combine and let it heat through for a few minutes. Season with salt to taste. Garnish generously with fresh cilantro before serving.