Put oven rack in middle position and preheat oven to 450°F. Pour butter into a large shallow baking pan (do not use glass) and tilt to coat bottom. Halve potatoes lengthwise, then rub a the cut garlic clove (cut side down) all over the cut side of the potato. Place a parsley leaf on cut side of each potato half and season with salt. Place potatoes, cut sides down, in baking pan. place the cloves of garlic around the potatoes and roast (do not turn over) until undersides are golden and potatoes are tender, 45 minutes.