Preheat oven to 425°F/220°C.
Dry the skin of the chicken with paper towel.
To a bowl, add the butter, rosemary, salt and pepper, mix well. Brush the butter all over the skin of the chicken.
Tie the legs together and tuck the wings under the breast.
To the bottom of a roasting pan place all the vegetables evenly and pour in the chicken stock. Set the chicken on top of the vegetables.
Roast the chicken on a low oven shelf for 40 minutes, reduce heat to 375°F/190°C and roast for 40 minutes more. If the skin is browning to quickly, turn the temperature down sooner.
To check for doneness, a thermometer inserted into the meatiest part, just above the leg should read 160°F/71°C.
Remove the chicken from the roasting pan, place on a cutting board and allow to rest for 20 minutes.
Meanwhile, strain the broth into a fat separator and add to a saucepan. Taste for seasoning, add more salt if needed (this depends on how salty your stock is).
Mix 1 tablespoon of cornstarch with 1 tablespoon of cold broth until dissolved.
Whisk into the gravy over medium heat and simmer until thickened stirring often to prevent sticking to the bottom of the pan.
Slice the chicken and serve with the gravy and your favorite sides.