1. Dice the onion and spread on the bottom of an aluminum pan. Place the thighs on top.
2. Whisk the mustard, olive oil, maple syrup, and salt and pepper together in a bowl.
3. Pour over the chicken. Throw in a few fresh sprigs of rosemary.
4. Cover tightly with foil and bake at 400 for 1 hour and 45 minutes. Uncover for the last 10 minutes.
5. Garnish with fresh rosemary. Enjoy!