Marinate the Chicken: In a large bowl, whisk together the ¾ cup yogurt, ginger garlic paste, lemon juice, salt, cumin, ground coriander, white pepper, and the optional minced green chili. Add the chicken pieces and toss until every piece is thickly coated. Cover and refrigerate for at least 30 minutes, or up to 8 hours for deeper flavour.
Blend the Green-Cashew Paste: Drain the soaked cashews and add them to a blender with the chopped onion, green chilies, coriander leaves, mint leaves, the ¼ cup yogurt, and ½ cup water. Blend until completely smooth and creamy — no flecks of cashew should remain. This paste is the entire base of the chicken afghani gravy, so take your time.
Sear the Chicken: Heat the ghee in a large, heavy pan or Dutch oven over medium-high heat. Shake the excess marinade off the chicken pieces (leave a thin coating) and sear in a single layer for 4–5 minutes per side until lightly golden at the edges. The chicken doesn't need to cook through yet — it will finish in the gravy. Remove and set aside.
Cook the Gravy Base: In the same pan, melt the butter over medium heat. Pour in the green-cashew paste, add the garam masala, white pepper, and salt, and cook for 8–10 minutes, stirring often, until the paste darkens slightly, thickens, and the fat begins to glisten at the edges. Pour in the 1 cup of water, bring to a gentle simmer, and cook 5 more minutes.
Combine and Simmer: Whisk in the heavy cream until fully incorporated. Add the seared chicken along with any accumulated juices. Cover and simmer gently for 12–15 minutes, stirring once or twice, until the chicken is cooked through (165°F / 74°C internal temperature) and the gravy is thick enough to coat the back of a spoon. Taste and adjust salt.
Finish and Serve: Take the pan off the heat. Crush the kasuri methi between your palms and stir it through the gravy along with a final swirl of cream. Garnish with fresh coriander and mint leaves, and serve hot with naan bread or jeera rice.