perfect roasted chicken

I make this recipe about once per week for the children I nanny. The chicken comes out tender and juicy every time and I love it because it doesn't take long to prepare and I can just pop it in the oven and go on to doing something else for an hour. It fills the house with the most wonderful aroma! You do not have to use all of the vegetables if you don't have them lying around. If all you have is an onion and a lemon to stuff it with, it will still come out great!

1 (5 to 6 pound) or 2kg roasting chicken
Kosher salt
Freshly ground black pepper
1 large bunch fresh thyme plus 20 sprigs
1 lemon, halved
1 head garlic cut in half crosswise
(1/4 stick) butter melted
1 large yellow onion
thickly sliced
4 carrots cut into 2-inch chunks
1 bulb of fennel, tops removed, and cut into wedges
Olive oil

Preheat the oven to 425 degrees F or 220degrees celcius. Remove the chicken giblets. Rinse the chicken inside and out. Remove any excess fat and leftover pin feathers and pat the outside dry. Liberally salt and pepper the inside of the chicken. Stuff the cavity with the bunch of thyme, both halves of lemon, and all the garlic. Brush the outside of the chicken with the butter and sprinkle again with salt and pepper. Tie the legs together with kitchen string and tuck the wing tips under the body of the chicken. Place the onions, carrots, and fennel in a roasting pan. Toss with salt, pepper, 20 sprigs of thyme, and olive oil. Spread around the bottom of the roasting pan and place the chicken on top. Roast the chicken for 1 1/2 hours, or until the juices run clear when you cut between a leg and thigh. Remove the chicken and vegetables to a platter and cover with aluminum foil for about 20 minutes. Slice the chicken onto a platter and serve it with the vegetables.