In a medium bowl, combine the chicken pieces with all the marinade ingredients (yogurt, 1 tbsp garlic, 1 tbsp ginger, 2 tsp garam masala, turmeric, 1 tsp cumin, cayenne, and 1 tsp salt). Mix well to coat all the chicken.

Cover and refrigerate for at least 15 minutes, or up to 2 hours for maximum flavor.

Heat 1 tbsp of oil in a large skillet or Dutch oven over medium-high heat. Add the chicken in a single layer (work in batches if necessary to avoid overcrowding).

Cook for 3-4 minutes per side, until golden brown and cooked through. Remove the chicken from the skillet and set aside.

In the same skillet, add the remaining 1 tbsp of oil. Add the diced onion and cook until softened, about 5-7 minutes.

Add the remaining garlic and ginger and cook for another minute until fragrant. Stir in the remaining spices (1.5 tsp garam masala, 1.5 tsp cumin, coriander) and cook for 30 seconds.

Pour in the crushed tomatoes, scraping up any browned bits from the bottom of the pan. Bring to a simmer and cook for 10 minutes, allowing the sauce to thicken slightly.

Reduce the heat to low and stir in the heavy cream. Return the cooked chicken to the skillet and stir to combine.

Simmer gently for 5 minutes for the flavors to meld together. Season with additional salt and pepper if needed. Garnish with fresh cilantro before serving or portioning.