- Preheat oven to 425 degrees F. In a large bowl, combine balsamic, honey, mustard, and garlic and season with salt and pepper. Whisk until combined. Add chicken thighs and toss until fully coated, then transfer to the fridge to marinate at least 20 minutes and up to 1 hour.
- Meanwhile, prep potatoes: In a medium bowl, add potatoes and rosemary and season with salt and pepper. Add 1 tablespoon olive oil and toss until combined. Set aside.
- In a large skillet over medium-high heat, heat remaining tablespoon oil. Add chicken and marinade and sear, skin side down, 2 minutes, then flip and sear 2 minutes more. Add potatoes to skillet, nestling them between chicken, and rosemary sprigs.
- Transfer to the oven and bake until potatoes are tender and chicken is cooked through, 20 minutes. (If potatoes need longer to cook, transfer chicken to a cutting board to rest and continue cooking until tender.)
- Serve chicken and potatoes with pan drippings.