Prep the chicken: Pat the chicken thighs dry with paper towels until the skin feels tacky, not wet. In a small bowl, combine the salt, pepper, and baking powder. Sprinkle this mixture evenly over both sides of the thighs, rubbing it gently into the skin. Place the thighs skin-side up on a wire rack set over a baking tray and refrigerate uncovered for at least 30 minutes — the skin will feel dry and slightly taut to the touch.

Preheat and prepare the pan: Preheat your oven to 200°C (400°F). Line a 9x13 inch baking dish with aluminium foil and set a wire rack inside the dish. This allows hot air to circulate underneath the chicken, which is key for even crisping.

Season the thighs: In a small bowl, mix the olive oil, minced garlic, smoked paprika, dried thyme, dried rosemary, and cayenne pepper if using. Brush this mixture all over the chicken thighs, coating every surface. The oil will help the skin brown and become shatteringly crisp.

Arrange and bake: Place the thighs skin-side up on the wire rack in the prepared dish, leaving a little space between each piece. Bake for 35 minutes. At this point, the skin should be golden and bubbling, and you'll hear a faint sizzle.

Brush with butter and finish: Remove the dish from the oven and brush the melted butter over the skin of each thigh. Return to the oven and bake for another 8–10 minutes. The skin will deepen to a rich amber colour and sound crackly when you tap it gently with a spoon. The internal temperature of the thickest thigh should read 74°C (165°F).

Rest and serve: Let the chicken thighs rest in the dish for 5 minutes. This allows the juices to redistribute and the skin to stay crisp. Transfer to a serving platter, sprinkle with fresh parsley or chives, and finish with a pinch of flaky sea salt. The skin will audibly crunch as you cut into it.