1. Preheat oven to 350°F. Combine 1 tablespoon parsley and pepper in small bowl. Press evenly onto all surfaces of beef roast.
2. Place roast, fat side up, on rack in shallow roasting pan. Insert ovenproof meat thermometer so tip is centered in thickest part of beef, not resting in fat. Do not add water or cover. Cut about 1/4 inch off top of each garlic head, exposing cloves. Remove outer papery skin, leaving head intact. Place in center of 12-inch square heavy-duty aluminum foil; drizzle each with 1 teaspoon oil. Bring two opposite sides of foil over garlic; seal with double fold. Fold in open ends to seal. Place alongside roast in pan. Roast beef in 350°F oven 1-3/4 to 2 hours for medium rare; 2 to 2-1/2 for medium doneness. Roast garlic 1-1/4 to 1-1/2 hours or until very soft and golden brown; set aside.
3. Remove roast when meat thermometer registers 135°F for medium rare; 150°F for medium. Transfer roast to carving board; tent loosely with aluminum foil. Let stand 15 to 20 minutes. (Temperature will continue to rise about 10°F to reach 145°F for medium rare; 160°F for medium.)
4. Meanwhile, squeeze garlic cloves from skins into small bowl; mash with back of spoon. Combine garlic, broth and sherry in medium saucepan; bring to boil. Cook 10 to 11 minutes or until reduced by half. Add half-and-half; reduce heat and bring to a gentle boil. Continue cooking 4 to 6 minutes or until sauce is reduced to 1 cup, stirring occasionally. Keep warm.
5. Carve roast into slices; serve with sauce. Garnish with additional parsley, as desired.