Season the chicken generously with salt, about 2 tbsp per side, and let it sit for 30 minutes. (The salt helps the chicken absorb the flavor and retain the moisture)
Stir 2 tablespoons of sea salt into the buttermilk to dissolve. Place the chicken in a gallon-size resealable plastic bag and pour in the buttermilk, rosemary, garlic, and Italian Seasoning.
Close the bag, massage the buttermilk all around the chicken, place on a rimmed plate, and refrigerate for 12 to 24 hours. Rotate the bag periodically (every 4-6 hours) to ensure every part of the chicken gets marinated.
Remove the chicken from the fridge an hour before you plan to cook it. Take the chicken out of the plastic bag and wipe off any excess buttermilk with a paper towel. Tightly tie together the legs with a piece of butcher’s twine (or string). Place the chicken on a wire rack and allow the chicken to come to room temperature while any excess buttermilk drips off the chicken.
Heat the oven to 425°F degrees with a rack set in the center position.
Transfer the chicken into a cast iron or shallow roasting pan or cast-iron skillet. If you want to add potatoes and vegetables, arrange them around the chicken.
Slide the pan to the back of the oven on the center rack. Rotate the pan so that the legs are facing the back left corner and the breast is pointing toward the center of the oven. Roast for 20 minutes.
After 20 minutes, the chicken should begin to brown. Lower the heat to 400°F and roast the chicken for an additional 10 minutes. Then, rotate the pan so the legs point towards the right corner of the oven and roast for 30 more minutes, or until the chicken is golden brown. The chicken is done when the juices run clear when cutting into the leg and an instant thermometer inserted into the thickest part reads 165°F.
Remove the chicken from the oven and let it rest for 10 minutes before carving.
Serve with your favorite side dishes and enjoy!