Prepare the Chicken: Pat the chicken thighs dry with paper towels. Trim away any large pieces of excess fat. If some thighs are substantially thicker than others, gently flatten the thickest areas so they cook more evenly.

Make the Tandoori Marinade: In a large bowl, combine the Greek yogurt, lemon juice, neutral oil, ginger, garlic, garam masala, Kashmiri chili powder, cumin, coriander, turmeric, salt, and black pepper. This mixture will create a flavorful coating for the chicken.

Check the Marinade Texture: Stir until completely smooth: The marinade should be thick enough to coat a spoon rather than run off like a thin liquid. This consistency is crucial for ensuring the chicken is well-coated and flavorful.

Coat the Chicken: Add the chicken thighs and turn them several times until every surface is generously coated with the yogurt mixture. This step ensures that the flavors penetrate the meat thoroughly.

Marinate: Cover the bowl and refrigerate for at least 4 hours. Avoid marinating much longer than 12 hours because prolonged exposure to the acidic yogurt and lemon can gradually soften the chicken's surface, affecting its texture.

Prepare the Oven: Remove the chicken from the refrigerator while the oven preheats. Heat the oven to 450°F (230°C). Line a large rimmed baking sheet with aluminum foil and place a wire rack on top to allow air circulation during roasting.

Arrange the Chicken: Lift each thigh from the marinade, allowing heavy excess marinade to drip back into the bowl. Arrange the chicken in a single layer on the rack with space between each piece. Discard the remaining raw-chicken marinade to prevent contamination.

Begin Roasting: Bake on the upper-middle oven rack for 12 minutes. The surface should begin drying and developing darker red-orange patches, indicating that the chicken is starting to cook through.

Turn the Chicken: Flip each thigh with tongs and continue baking for another 8 to 10 minutes. This ensures even cooking and browning on both sides of the chicken.

Check for Doneness: Insert an instant-read thermometer into the thickest section of the largest thigh. The chicken must reach at least 165°F (74°C). The exterior should look browned and slightly caramelized rather than wet with marinade, indicating it is fully cooked.

Brush with Butter or Ghee: Lightly brush the cooked chicken with the melted butter or ghee. This adds richness and encourages additional browning during the final broil, enhancing the flavor and texture.

Broil for Charred Edges: Switch the oven to BROIL on high. Broil the chicken for 1 to 3 minutes, watching continuously, until several edges develop dark, lightly charred spots. Do not walk away, as the yogurt marinade can brown rapidly, and you want to achieve the perfect char without burning.

Rest the Chicken: Transfer the chicken to a clean platter and let it rest for 10 minutes before slicing or serving. This resting period allows the juices to redistribute, ensuring moist and tender chicken.

Garnish and Serve: Sprinkle with fresh cilantro and serve with lemon wedges and sliced red onion, if desired. These garnishes add freshness and brightness to the dish.