Marinate the Chicken: In a medium bowl, combine the chicken pieces with all the marinade ingredients: Greek yoghurt, lemon juice, ginger-garlic paste, turmeric, garam masala, Kashmiri chilli powder, and salt. Mix thoroughly until every piece of chicken is well-coated. Cover and refrigerate for at least 1 hour, or up to 8 hours for the best flavour.

Cook the Chicken: Heat 1 tablespoon of the ghee or butter in a large, heavy-bottomed frying pan or skillet over a medium-high heat. Add the marinated chicken pieces in a single layer (you may need to do this in two batches). Cook for 3-4 minutes per side, until the chicken has some lovely charred spots and is cooked through. Remove the chicken from the pan and set aside.

Start the Sauce Base: In the same pan, add the remaining tablespoon of ghee. Lower the heat to medium and add the finely chopped onion. Cook for 8-10 minutes, stirring occasionally, until the onion is soft, translucent, and just beginning to turn golden. This slow cooking builds a sweet foundation for our sauce.

Bloom the Spices: Add the ginger-garlic paste to the onions and cook for another minute until fragrant. Then, add the ground cumin, ground coriander, and Kashmiri chilli powder. Stir constantly for about 30 seconds until the spices release their aroma. This step is crucial for developing a deep flavour.

Simmer the Gravy: Pour in the tin of chopped tomatoes and add the 250ml of water, salt, and optional sugar. Bring to a simmer, then reduce the heat to low, cover the pan, and let it cook gently for 15 minutes. This allows the tomato flavour to deepen and mellow.

Blend for Smoothness: While the sauce simmers, drain the soaked cashews. Transfer the tomato and onion mixture from the pan to a high-speed blender. Add the drained cashews. Blend on high for 1-2 minutes until the sauce is completely smooth and velvety. This is the secret to a restaurant-quality creamy texture.

Finish the Sauce: Pour the blended sauce back into the same pan over a low heat. Add the cubed 50g of butter and stir until it has completely melted into the gravy. What works best for me is adding the butter off the heat initially to prevent it from splitting.

Combine and Finalise: Return the cooked chicken pieces to the pan with the sauce. Stir gently to coat. Let it simmer for 2-3 minutes for the flavours to meld. Crush the kasuri methi between your palms and sprinkle it over the curry. Stir in the double cream, then turn off the heat immediately. Do not let it boil after adding the cream. Serve hot.