In a large bowl, combine yogurt, minced garlic, ginger, garam masala, paprika, salt, and lemon juice. Mix well until smooth. Add the chicken pieces and coat thoroughly so all pieces are evenly covered. Cover and let marinate for at least 30 minutes at room temperature, or up to overnight in the refrigerator for deeper flavor.

Heat a large pan or pot over medium-high heat. Add 1 tablespoon oil and a small knob of butter. Once hot, add the marinated chicken in batches, making sure not to overcrowd the pan. Cook each batch for about 4–5 minutes, turning occasionally, until lightly browned on the outside (the chicken does not need to be fully cooked at this stage). Remove and set aside.

In the same pan, reduce heat to medium and add 4 tablespoons butter. Once melted, add the finely chopped onion. Cook for 5–7 minutes, stirring occasionally, until the onion is soft, translucent, and slightly golden. Add the minced garlic and ginger, and cook for another 1–2 minutes until fragrant.

Add garam masala, turmeric, paprika, cumin, and chili powder (if using) directly into the butter and onion mixture. Stir continuously and cook for 1–2 minutes to toast the spices and bring out their flavor. Do not skip this step—it builds the base flavor of the dish.

Stir in the tomato paste and cook for 1–2 minutes to deepen its flavor. Then add the crushed tomatoes and sugar. Mix well and bring to a gentle simmer. Let the sauce cook uncovered for 10–15 minutes, stirring occasionally, until it thickens slightly and the flavors combine.

For a smooth, restaurant-style texture, carefully blend the sauce using an immersion blender directly in the pot, or transfer to a blender in batches. Blend until completely smooth, then return to the pan.

Return the partially cooked chicken (and any juices) to the pan. Stir to coat the chicken in the sauce. Simmer over medium-low heat for 10–15 minutes, or until the chicken is fully cooked through and tender.

Lower the heat to low. Slowly stir in the heavy cream and milk mixture, followed by 1–2 tablespoons butter. Stir continuously until fully incorporated and the sauce becomes smooth and creamy. Do not allow the sauce to boil after adding the cream.

Taste the sauce and adjust salt as needed. If using, crush the kasuri methi between your hands and stir it in. Add a small squeeze of fresh lemon juice to brighten the flavor. Let the dish simmer gently for 2–3 more minutes.

Serve

Serve hot over basmati rice or with naan. Spoon extra sauce over the top for serving.