2. Rinse the chicken with cold water, pat dry and season with salt and pepper inside and out.
3. Stuff the cavity with the rosemary, thyme, bay leaf and peeled garlic. Also put a few pieces of onion, carrot and celery into the cavity.
4. Scatter the rest of the onions, carrots and celery on the bottom of a roasting pan. Place the chicken on top of the vegetables. Squeeze juice from the lemon all over the chicken and add the lemon half to the cavity.
5. Place in the oven. After 15 minutes turn the heat down to 350°F. Roast the chicken for an additional 45 minutes to 1 hour, until it's golden brown and crisp and the juices run clear when the thigh is pierced with a sharp knife.
6. Transfer the chicken to a serving platter and let rest for about 10 minutes. Remove the skin and discard. Carve the chicken into serving pieces.
For the garlic mashed potatoes:
1. Meanwhile, place the garlic bulb in an ovenproof dish and drizzle with olive oil. Once the oven has been turned down to 350°F, place the dish, uncovered, in the oven for 15-20 minutes until the garlic is golden brown and soft.
2. Remove from the oven and let cool.
3. Peel the potatoes and cut them in half. Place them in a pot and cover with cold water. Bring to a boil over high heat and simmer until the potatoes are tender when pricked with a fork, about 30 minutes, depending on the size of the potatoes. Drain.
4. Bring the stock to a boil, and turn down to a simmer.
5. Squeeze the roasted garlic bulb to release the roasted garlic in each clove. Mash the garlic with a fork and throw the skins away.
6. Mash the potatoes with a potato masher or fork, or use a food mill. Add the roasted garlic. Slowly add the stock until the desired consistency is reached.
7. Adjust the salt and pepper to taste and serve alongside the chicken.