Preheat oven to 450 degrees.

Rinse chicken under cool running water and pat dry with paper towels; place it on the rack of a large roasting pan, breast side up. Using your fingers, gently separate the skin from the meat and rub the butter evenly all over the flesh of the chicken. Sprinkle the outside of the chicken evenly with salt and pepper.

Meanwhile, in a large bowl, combine carrots, leeks, mushrooms, cauliflower, rosemary, salt and pepper; drizzle with olive oil then toss to blend well. Arrange vegetables around the chicken in the roasting pan and roast, uncovered, for 1 to 1 1/2 hours, basting at least twice with pan juices.

Chicken is cooked through when internal temperature reaches 160 degrees and juices run clear. Place chicken on a cutting board and allow it to rest for 5 to 10 minutes before carving. Serve with roasted vegetables.