Marinate the Chicken: In a large bowl, toss the chicken pieces with the ginger garlic paste, turmeric, Kashmiri red chili powder, lemon juice, and salt until evenly coated. Cover and refrigerate for at least 30 minutes, or up to 4 hours.
Dry-Roast and Grind the Spices: Heat a dry skillet over medium heat. Add the black peppercorns, fennel seeds, cumin seeds, coriander seeds (if using), and dried red chilies. Toast for 2–3 minutes until aromatic. Cool for 2 minutes, then grind to a coarse powder.
Temper in Coconut Oil: Heat 3 tablespoons of coconut oil in a wide, heavy kadai over medium-high heat. Add the mustard seeds and let them pop for 20–30 seconds. Add the halved shallots and 2 sprigs of curry leaves. Sauté for 8–10 minutes until deep golden.
Add the Chicken and Masala: Add the marinated chicken to the kadai and toss to coat. Sprinkle over all of the freshly ground varuval masala. Cook over medium-high heat for 5 minutes, then lower heat, cover, and cook for 15–18 minutes until cooked through (165°F / 74°C) and moisture has dried out.
The Dry-Fry Finish: Uncover, raise heat to high, drizzle over the remaining 1 tablespoon of coconut oil. Toss in the remaining sprig of curry leaves. Dry-fry for 4–5 minutes until charred, crispy edges develop.
Serve: Transfer to a warm platter, squeeze lemon wedges over the top, and serve immediately while the spice crust is still crackling.