In a large bowl, combine chicken pieces with yogurt, ginger-garlic paste, lemon juice, turmeric, chili powder, garam masala, and salt. Mix well to coat all the chicken.

Cover the bowl and refrigerate for at least 30 minutes, or preferably for 2-4 hours.

Heat 1 tablespoon of ghee or butter in a large skillet or pot over medium-high heat. Add the marinated chicken and cook in batches until lightly browned on all sides and cooked through. Set the cooked chicken aside.

In the same skillet, add the remaining 1 tablespoon of ghee or butter. Sauté the chopped onion until it turns translucent and lightly golden.

Add ginger-garlic paste to the onions and cook for another minute until fragrant.

Pour in the crushed tomatoes and water. Bring the mixture to a simmer, then reduce heat and let it cook for 10-15 minutes, stirring occasionally, until the sauce thickens and the raw tomato flavor disappears.

Drain the soaked cashews and add them to the tomato mixture. Transfer the sauce to a blender and blend until completely smooth. If needed, add a little more water to achieve desired consistency.

Return the smooth sauce to the skillet. Stir in garam masala, sugar, and salt. Bring the sauce to a gentle simmer.

Add the cooked chicken to the sauce and stir to coat. Let it simmer for 5-7 minutes, allowing the flavors to meld.

Stir in the heavy cream and cook for another 2-3 minutes, ensuring the sauce is heated through but not boiled.

Garnish with fresh cilantro and serve hot with naan bread or basmati rice.