With a small knife, pierce top of roast. Force garlic slices into the slits. Sprinkle the roast with salt and pepper. Place bay leaves in the bottom of the roasting tin, and set roast on top of bay leaves, fat side up. Mix vinegar and thyme in a small bowl, and pour over the top of the roast.
Roast for 3 hours, until no longer pink, or until an internal temperature of 70 C is reached. Baste the roast frequently while it is cooking. Let it rest for 15 minutes covered with foil before slicing.