Cut the chicken into bite-sized pieces, approximately 1 inch in size. Alternatively, if using bone-in chicken, it may be left whole.
Place the chicken into a bowl and sprinkle with ½ teaspoon salt, ½ teaspoon ground cumin, ¼ teaspoon ground coriander, ¼ teaspoon ground turmeric, black pepper, and cayenne pepper if using. Toss thoroughly to coat the chicken in the spices. Set aside to marinate for a minimum of 20 minutes. If preparing ahead, cover and refrigerate for up to 24 hours.
In a blender or food processor, combine the garlic cloves, ginger, chopped onion, and ½ cup of water. Process until the mixture is mostly smooth. An immersion blender with a cup attachment may also be used.
Heat the oil or ghee in a wide, lidded skillet over medium-high heat. Arrange the marinated chicken pieces in a single layer and brown on both sides, about 2 to 3 minutes per side. Once browned, remove the chicken and set it aside. Leave the skillet on the heat.
Pour the blended onion-ginger mixture into the hot skillet. Cook, stirring regularly, until the liquid evaporates, approximately 5 minutes.
Sprinkle in the remaining ½ teaspoon ground cumin, ½ teaspoon ground coriander, and ¼ teaspoon ground turmeric. Stir and let cook for about 20 seconds until fragrant. Add the tomato paste and reduce the heat to medium-low. Stir and cook for an additional minute.
Begin incorporating the yogurt, one tablespoon at a time, stirring thoroughly after each addition to prevent curdling.
Return the chicken and any accumulated juices to the skillet. Pour in the remaining 1 cup of water along with ¾ teaspoon salt. Bring to a gentle boil, then reduce the heat to low, cover with a lid, and simmer for 20 minutes.
Uncover the skillet and stir in the Garam Masala and heavy cream. Taste the sauce and adjust the seasoning by adding the final ¼ teaspoon of salt if needed. Increase the heat to medium-high and cook, stirring occasionally, until the sauce has thickened and reduced, about 3 to 5 minutes.
Garnish with chopped cilantro leaves if desired, and serve immediately.