In a small sauce pot add garlic cloves and olive oil and place over low heat. Cook garlic for 45 minutes to 1 hour never letting the oil get higher than a bare simmer. This will keep olive oil from burning and allow garlic to cook gently. Turn oil off when garlic reaches a light brown color and is soft.
Once garlic is cooked and completely cooled, scoop out with a slotted spoon (reserve olive oil for future use). Place garlic, salt, pepper and thyme into a food processor and pulse until it forms a smooth paste.
Rub roast completely with garlic paste. In a roasting pan place carrots and celery down as a rack and place seasoned roast on top of vegetables.
Place roast into oven and roast for 2 - 2 1/2 hours or until internal temperature reads 135°F.
Remove from oven and allow to rest for at least 20 minutes before carving. Pour pan juices over each slice for extra flavor.