Remove the neck and any giblets from the chicken cavity; reserve or discard them.
Place a gallon resealable bag in a large bowl and set the chicken into the bag breast toward the bottom and legs toward the opening.
In a mixing bowl whisk together the buttermilk, kosher salt, cracked black pepper, minced garlic, minced rosemary, and minced thyme until combined, about 30 seconds.
Pour the buttermilk mixture over the chicken, pouring some into the cavity as well, then seal the bag after pressing out excess air and rub the marinade over the chicken.
Refrigerate and marinate at least 12 hours and up to 24 hours, turning the chicken once halfway through if possible (otherwise marinate breast side down).
When ready to roast, preheat the oven to 400°F (200°C). Remove the chicken from the marinade, pour out and discard marinade from the cavity, and scrape off excess buttermilk mixture.
Transfer the chicken to a 12-inch cast iron skillet or small roasting pan. Tuck the wings underneath and optionally truss the legs with kitchen twine for presentation.
Place the pan in the center of the oven and roast for 40 minutes, then rotate the pan to the opposite side for even browning.
Continue roasting until the thigh reaches 175°F and the breast 160°F in their thickest parts, about 30 to 45 minutes more; tent with foil if the skin is browning too quickly.
Transfer the chicken to a cutting board and let rest 15 minutes, then carve and sprinkle slices with a little salt if desired.