Pat the chicken completely dry. Cut 2-3 deep diagonal slits into each piece down to the bone so marinade can sink in deep.
Rub lemon juice, salt, and 1 tsp of Kashmiri chili powder into the chicken. Let rest for 15-20 minutes to tenderize.
In a separate bowl, whisk Greek yogurt, ginger-garlic paste, mustard oil, remaining Kashmiri chili, garam masala, cumin, and kasuri methi into a thick paste.
Coat the chicken thoroughly in the yogurt paste. Cover and refrigerate for at least 4 hours, or overnight for optimal flavor.
Preheat oven to 220°C (425°F). Place chicken on a greased wire rack over a foil-lined baking sheet. Roast for 20-22 minutes.
Brush with melted butter. Turn oven to broil (high) and cook for 3-5 minutes until you see beautiful charred spots on the edges.