Trim any excess fat and skin from thighs. Season chicken on both sides with salt and pepper, ideally the day before you intend to cook. Mix butter, pressed garlic, and dried herbs of choice, gently loosen skin from thighs, and spread butter mixture under skin. Refrigerate overnight or let rest 1 hour at room temperature.

Preheat oven to 350ºF.

Toss potatoes, onion, tomatoes, and garlic with olive oil and spread in the bottom of a 10-inch cast-iron skillet (if you’re not watching your fat intake, by all means tuck that excess chicken fat and skin in with the potatoes). Arrange chicken thighs on top of vegetables, skin-side up, transfer to the oven, and roast for 1 hour. Serve at once.