Season the chicken thighs evenly on both sides with sea salt and black pepper.
Heat the olive oil in a large deep skillet or Dutch oven over medium-high heat.
Place the chicken in the skillet and sear for 4-5 minutes per side until a golden-brown crust forms, then remove and set aside.
In the same pan, add the chopped carrots, parsnips, and onions, sautéing for 5-7 minutes until they begin to soften and caramelize.
Stir in the minced garlic, thyme, and the rosemary sprig, cooking for 1 minute until fragrant.
Pour in the chicken broth, using a wooden spoon to scrape up any browned bits from the bottom of the pan.
Return the chicken thighs to the skillet, nestling them into the vegetables and liquid.
Reduce heat to low, cover with a lid, and simmer for 20-25 minutes until the chicken is tender and the vegetables are soft.
Remove the rosemary sprig before serving the chicken and vegetables with the pan juices.