Arrange a rack in the center of your oven, and preheat to 425 °F/ 220 °C.
Take a large oven-safe skillet (I use a cast-iron skillet) and rub a small amount of oil onto the pan (one tablespoon should be enough); set aside.
Thoroughly pat-dry the whole chicken with paper towels which will help with browning.
Transfer the chicken breast side up to the reserved oven-safe skillet.
Season every surface of the chicken generously with salt, including inside the wings.
Rub some salt inside the cavity. I use 2 to 3 teaspoons of salt to season the whole chicken. As you season the chicken in the skillet, some of the oil will rub off the chicken, which is okay.
Cut the head of garlic crosswise in half. Arrange one half cut side down in the skillet (I always use the bottom part). Take the garlic pieces out of the other (top) half, and arrange them inside the chicken.
Arrange the onion pieces around the chicken in the oven-safe skillet and stuff some inside the cavity.
With the chicken breast facing up, slice partly through the skin that connects the legs to the breast. Season the meat inside also with some salt. You will use these openings for the Brie filling.
Take the pieces of Brie and arrange them between the chicken legs, wings, and a few pieces inside the cavity.
Now arrange the grapes around the chicken and on top of the onions and garlic in the oven-safe skillet. Stuff some pieces inside the cavity.
Season the onions and grapes with a few extra pinches of salt.
Then season the chicken evenly with Italian seasoning.
Season everything generously with black pepper.
Drizzle ¼ cup of extra-virgin olive oil over the ingredients, nicely coating the chicken.
Arrange the fresh Rosemary sprigs in the pan around the chicken.
Transfer to the oven and roast until the chicken is beautifully browned and done. Count 15 minutes per pound of chicken, so for a 4 pound of chicken, roast for 1 hour. To check for doneness, I carefully remove the skillet from the oven and check between the cut leg joints. It needs more time if you see any pinkish colors.
Let the cast-iron roast chicken rest for a few minutes before carving and serving.
The pan juices will be incredibly flavorful and should be served together with the meat or any side dishes like mashed potatoes or Mashed cauliflower. Remove the Rosemary leaves. Crumble some of the dried needles and place them back into the pan (optional).
This beautiful cast-iron roasted chicken recipe is unique enough to serve on festive occasions—think chicken for Thanksgiving or Christmas!