Sear the Chicken: Heat 1 tablespoon of butter with the oil in a large, heavy skillet or Dutch oven over medium-high heat. Add the marinated chicken in a single layer (work in batches if needed) and sear for 4–5 minutes per side until lightly charred at the edges. The chicken doesn't need to cook through yet — it will finish in the gravy. Remove and set aside.

Build the Tomato Gravy: In the same pan, melt the remaining 2 tablespoons of butter. Add the chopped onion and cook for 6–8 minutes until soft and golden. Stir in the ginger garlic paste and cook 1 minute until fragrant. Add the chopped tomatoes, cashews, Kashmiri red chili powder, turmeric, garam masala, and salt. Pour in the water, bring to a simmer, then cover and cook for 12–15 minutes until the tomatoes break down completely.

Blend Until Silky: Let the gravy cool slightly, then blend until completely smooth using an immersion blender (or a regular blender in batches — vent the lid so steam escapes). For an ultra-silky restaurant-style finish, strain the gravy through a fine-mesh sieve back into the pan — this one step makes a huge difference.

Combine and Finish: Return the gravy to medium-low heat. Stir in the heavy cream, crushed kasuri methi, and the final tablespoon of butter. Add the seared chicken pieces along with any accumulated juices. Simmer gently for 8–10 minutes until the chicken is cooked through (165°F / 74°C internal temperature) and the gravy thickens enough to coat the back of a spoon. Taste and adjust salt.

Serve: Drizzle with a swirl of cream, sprinkle with fresh cilantro, and serve hot with naan bread or basmati rice.