Pat the chicken thighs with a paper towel to remove excess moisture and help the skin crisp.
Sprinkle 1 teaspoon of salt and ½ teaspoon pepper evenly over the top of the chicken.
Use a pastry brush to brush the tops with 1 tablespoon olive oil.
Set the chicken thighs skin side up onto a large rimmed baking sheet, covered in foil.
Bake in the oven for 20 minutes.
Add the carrots, potato, and onion to a large bowl.
Drizzle with 2 tablespoons olive oil.
Toss the vegetables, coating them with the oil. Sprinkle 1 teaspoon salt, ½ teaspoon black pepper, and the rosemary evenly over the vegetables.
Toss once again to coat.
Remove the sheet pan from the oven.
Transfer the chicken onto a plate.
Drain and discard the juices from the pan. Add the vegetables and the chicken back into the pan in an even layer. Reduce the heat to 375° F.
Return the pan to the oven and bake for 35 to 45 minutes, or until internal temperature of the chicken reaches 165° F.
Remove from the oven.
Serve.
Notes
For maximum presentation arrangement arrange the vegetables on the bottom and the chicken on top of the vegetables. Garnish with a sprig of fresh rosemary.