In a bowl, season chopped carrots, sweet potatoes, and sliced apples with 2 tbsp oil, salt, and pepper to taste. Toss together.
Season chicken thighs with a generous amount of salt and pepper on all sides. Over medium to high heat, sear the chicken in with skin side down * for about 2 - 3 minutes until golden and slightly crispy.
Remove the chicken and set it on a piece of paper towel.
Combine apple cider, dijon mustard, 1/2 tbsp minced rosemary in the same pan, bring it to boil, and simmer for 45-60 seconds to reduce it slightly.
Add chicken skin up, carrots, sweet potatoes, and apple back in the skillet. Then place the rest of the rosemary sprigs on top.
Bake 20 minutes or until chicken is cooked (internal temperature reaches 165 F) and sweet potatoes become tender.
Enjoy!
Notes
* If your cast iron skillet is pre-greased, you do not need to add additional oil, the oil from chicken thighs will be enough. Otherwise, heat up 1/2 tbsp - 1 tbsp oil in the skillet to prevent the chicken skin from sticking.