With the rack in the middle position, preheat the oven to 265 °F (130 °C).
On a work surface, combine the garlic, salt and pepper by crushing them with the flat part of a chef's knife, until garlic forms a paste. Rub the garlic paste on all sides of the roast. Place the roast in a baking dish. Roast for about 4 hours and 30 minutes, uncovered.