Dry Brine: Pat the chicken (1 whole) completely dry with paper towels. Sprinkle the kosher salt (1 tablespoon) evenly over the entire chicken, including inside the cavity. Place the chicken on a wire rack set over a baking sheet and refrigerate uncovered for 8–24 hours.
Prepare the Chicken: Remove the chicken from the refrigerator 30–45 minutes before roasting. Preheat the oven to 425°F (218ºC). If needed, pat the skin dry once more. Make the Herb Butter: In a small bowl, combine the softened butter (6 tablespoons), black pepper (1 teaspoon), garlic powder (1 teaspoon), onion powder (1 teaspoon), paprika (1 teaspoon), thyme (1 teaspoon), rosemary (1/2 teaspoon), and sage (1/2 teaspoon) until smooth. Let the butter rest for 10–15 minutes to allow the dried herbs to hydrate.
Season the Chicken: Carefully loosen the skin over the breasts and thighs without tearing it. Spread about three-quarters of the herb butter underneath the skin, then rub the remaining butter over the outside of the chicken and inside the cavity.
Prepare Cavity: Stuff the cavity with the lemon (1), onion (1/2), celery (1), garlic (1), and rosemary sprigs (2-3 sprigs).
Arrange Chicken: Tuck the wings and use some kitchen string to tie the drumsticks together.
Roast: Place the chicken breast-side up in a roasting pan, large cast iron skillet, or oven-safe baking dish. Pour the chicken broth (1 cup) into the pan around the chicken, taking care not to wet the skin.
Roast: Roast for 20 minutes at 425°F (218ºC), then reduce the oven temperature to 375°F (190ºC) without opening the oven. Continue roasting for 50–70 minutes, or until the thickest part of the breast reaches 158–160°F (70-71ºC) and the thighs reach about 175°F (79ºC).If additional browning is needed, broil for 1–2 minutes while watching carefully. Basting is optional and should only be done once during the final 20–30 minutes of cooking. Make the Gravy: Pour the pan drippings into a fat separator or measuring cup and let the fat rise to the top. Measure 2 tablespoons of the chicken fat and add it to a saucepan, using butter if needed to make 2 tablespoons. Whisk in the flour and cook over medium heat for 1–2 minutes. Gradually whisk in 1 1/2 cups chicken broth and the defatted pan drippings. Add the Worcestershire sauce and bring to a gentle simmer. Cook, whisking frequently, until the gravy thickens, about 3–5 minutes. Add additional chicken broth as needed to reach your desired consistency. Season with salt and black pepper to taste and stir in the fresh thyme, if using.