In a mini food processor or blender, mince garlic, rosemary, salt and pepper. Slowly add olive oil while continuing to process into a thick paste.
Place the roast in a roasting pan, fat side up and bone side down. Rub the paste all over the meat (if you want a milder version, reduce the amount of paste you rub on the roast). Let stand for 2-3 hours at room temperature (or overnight in the refrigerator – let the roast return to room temperature before baking).
Preheat oven to 350 degrees. Bake roast until it reaches an internal temperature of 100 degrees (approximately 1 hour and 20 minutes) in the center of the roast. While you are roasting, prepare the potatoes.