01 - Preheat your oven to 220°C (425°F).
02 - In a small mixing bowl, combine the softened butter, minced garlic, chopped parsley, thyme, rosemary, lemon zest, salt, and black pepper. Mix thoroughly to create a uniform herb butter.
03 - Pat the chicken thoroughly dry with paper towels. Carefully separate the skin from the breast and thigh meat, then spread half of the prepared herb butter underneath the skin. Rub the remaining herb butter evenly over the entire surface of the chicken.
04 - Place the quartered lemon and onion pieces inside the chicken's cavity.
05 - Scatter the cut carrots and celery in the bottom of a roasting pan. Position the chicken on top of the vegetables, breast-side up. Drizzle the chicken with olive oil and pour the chicken broth into the pan.
06 - Tie the chicken legs together securely using kitchen twine. Tuck the wing tips underneath the body of the chicken to prevent them from burning.
07 - Roast the chicken for 20 minutes at 220°C (425°F). Reduce the oven temperature to 190°C (375°F) and continue roasting for an additional 55–60 minutes. The chicken is done when its juices run clear and a meat thermometer inserted into the thickest part of the thigh registers 75°C (165°F).
08 - Allow the roasted chicken to rest for 10–15 minutes before carving. Serve with the roasted vegetables and pan juices.