Pat chicken thighs dry and place on a baking sheet, skin side up. Put in the fridge, uncovered, for anywhere from 8 hours to overnight. Remove from the fridge 45 minutes before cooking.

Preheat oven to 500°. Spread onions in the bottom of a shallow baking dish that can snugly fit the chicken thighs. Top with the garlic, lemon slices, thyme & rosemary.

Remove the chicken from the baking sheet and place on paper towels. Pat dry again. Sprinkle both sides of the chicken thighs with the salt and pepper, and place on top of the onion/garlic mixture. Use your hands to push all of the onions etc. underneath the chicken.

Bake for 40 - 50 minutes or until the juices run clear when pierced with a knife. If the chicken skin isn't crispy enough, you can finish under the broiler for a few minutes.

Discard the lemon & herbs sprigs. Serve the chicken with the onion/garlic mixture.