Prepare the chicken marinade. In a medium bowl, combine the chicken pieces, 125ml (0.5 cup) of plain yogurt, 15ml (1 tbsp) of lemon juice, 15g (1 tbsp) of ginger-garlic paste, 5g (1 tsp) of garam masala, 2.5g (0.5 tsp) of turmeric powder, 2.5g (0.5 tsp) of red chili powder, and 5g (1 tsp) of salt. Mix thoroughly to ensure each chicken piece is well-coated.

Marinate the chicken. Cover the bowl with plastic wrap and refrigerate for at least 30 minutes, or ideally for 2-4 hours (or even overnight for deeper flavor).

Prepare the cashew paste. Drain the soaked cashews and transfer them to a blender. Add about 60ml (0.25 cup) of water and blend until a very smooth paste forms. Set aside.

Sear the chicken. Heat 15ml (1 tbsp) of vegetable oil or ghee in a large, heavy-bottomed pan or Dutch oven over medium-high heat. Working in batches to avoid overcrowding, sear the marinated chicken pieces for 2-3 minutes per side until lightly browned. The chicken does not need to be cooked through at this stage. Remove the seared chicken from the pan and set aside.

Sauté the aromatics. In the same pan, reduce the heat to medium. Add 50g (3.5 tbsp) of butter and the remaining 15ml (1 tbsp) of vegetable oil or ghee. Once the butter is melted and foaming, add the green cardamom pods, cloves, cinnamon stick, and bay leaf. Sauté for about 30 seconds until fragrant.

Add the chopped onions to the pan. Cook, stirring occasionally, until they soften and become translucent, about 5-7 minutes. Be careful not to brown them too much.

Stir in the remaining 15g (1 tbsp) of ginger-garlic paste and cook for another minute until fragrant.

Add the ground spices. Stir in the remaining 5g (1 tsp) of turmeric powder, 5g (1 tsp) of red chili powder, 10g (2 tsp) of coriander powder, and 5g (1 tsp) of cumin powder. Cook for 30 seconds, stirring constantly, until the spices are fragrant.

Add the pureed tomatoes to the pan. Stir well to combine with the spices and onions. Bring the mixture to a simmer, then reduce the heat to low, cover, and cook for 15-20 minutes, stirring occasionally, until the tomato mixture thickens and the oil begins to separate from the sides.

Remove the whole spices (cinnamon stick, bay leaf, cardamom pods, cloves) from the sauce. This is optional but recommended for a smoother sauce. You can do this with a slotted spoon.

Blend the sauce until smooth. Carefully transfer the tomato mixture to a blender (or use an immersion blender directly in the pot). Blend until completely smooth. Return the smooth sauce to the pan.

Incorporate the cashew paste. Stir the prepared cashew paste into the smooth tomato sauce. Cook for 2-3 minutes, stirring constantly, until the sauce thickens slightly.

Add the seared chicken back to the pan. Stir to coat the chicken pieces in the sauce. Add the remaining 125ml (0.5 cup) of plain yogurt and 15ml (1 tbsp) of lemon juice. Stir well to combine.

Simmer the curry. Bring the sauce to a gentle simmer over low heat. Cover the pan and cook for 15-20 minutes, or until the chicken is cooked through and tender. Stir occasionally to prevent sticking.

Finish the sauce. Stir in the remaining 50g (3.5 tbsp) of butter, heavy cream, Kasuri Methi (crushed between your palms), and sugar. Cook for another 2-3 minutes until the butter is melted and the sauce is creamy and heated through. Do not boil after adding cream.

Taste and adjust seasoning. Add salt if needed. Remove from heat.

Serve hot. Garnish with fresh chopped cilantro. Butter chicken is traditionally served with naan, roti, or basmati rice.