Preheat oven to 400 F. Pat dry each chicken thigh with a paper towel completely before adding seasoning. This helps create extra crispy skins when searing.
In a medium bowl, add Italian seasoning, paprika, salt, and pepper mix well to combine. Generously rub ¾ of the seasoning mixture all over the chicken thighs, on both sides.
Add in onions, garlic, potatoes, and carrots to the bowl with the remaining seasoning mixture. Toss to combine.
Melt the butter in a cast-iron skillet over medium high heat for 1-2 minutes until hot. Place the chicken thighs with the skin side down on the skillet, and sear for 2-3 minutes until the skin turns brown and crispy. Flip the chicken over and cook on the other side for another 2 minutes. Remove the chicken thighs from the skillet and place them on a plate.
On the same skillet, add the vegetables and stir well to combine. Cook for 3-4 minutes until onions are soft and start to slightly brown. Remove from heat and place chicken thighs on top, skin side up.
Transfer the skillet into the preheated oven and bake for 30-40 minutes, until the internal temperature for the chicken thighs reaches 165F. Remove the skillet from the oven and let it rest for 10 minutes before serving.
