Keeping cloves intact, cut 1 inch off top of garlic bulb. Sprinkle oil over garlic. Wrap loosely with foil and bake in a 350 oven for one hour. Squeeze garlic from skin; discard skins. Cook potatoes until tender; drain and pare. Mash while hot. Add garlic and butter; mix until butter melts. Add rosemary, salt and pepper. Stir in broth, a little at a time; beat till smooth and fluffy, adding broth as needed. Stir in parmasan cheese. Makes 8 servings.