Cut slices down the length of bread loaf at 1" intervals without cutting all the way through. Rub slices and top of loaf with cut sides of garlic halves.
Combine butter, garlic, parsley and Parmesan cheese into a small bowl. Spread butter mixture between bread slices and on top of loaf.
Wrap bread in foil, leaving top partially uncovered. Bake until heated through, about 15 minutes.