In a medium bowl, combine the chicken pieces with all the marinade ingredients (yogurt, 1 tbsp ginger garlic paste, turmeric, 1 tsp garam masala, chili powder, and 1 tsp salt). Mix well to coat. Cover and refrigerate for at least 30 minutes or up to 8 hours.

Heat oil in a large skillet or pan over medium-high heat. Add the marinated chicken in a single layer (work in batches if needed). Cook for 3-4 minutes per side, until browned and cooked through. Remove the chicken from the skillet and set aside.

In the same skillet, melt 2 tablespoons of butter over medium heat. Add the chopped onion and cook until soft, about 5-7 minutes.

Stir in 1 tbsp of ginger garlic paste and cook for 1 minute until fragrant. Add the ground coriander, cumin, and 1 tsp garam masala. Cook for 30 seconds, stirring constantly.

Pour in the tomato puree, add the raw cashews, and season with a pinch of salt. Bring to a simmer and cook for 10-12 minutes, stirring occasionally.

Carefully transfer the hot mixture to a high-speed blender. Blend until the sauce is completely smooth and velvety. Return the sauce to the skillet.

Stir the heavy cream and sugar (if using) into the sauce. Bring to a gentle simmer. Add the cooked chicken back to the pan and stir to combine.

Let the curry simmer over low heat for 5-10 minutes. Stir in the remaining 2 tablespoons of butter.

Take the dried fenugreek leaves (kasoori methi) and crush them between your palms over the skillet. Stir into the sauce. Serve hot with naan or rice.