In the bowl of a stand mixer fitted with the whisk attachment add the butter, garlic and parsley and mix on medium-low speed until thoroughly combined and soft.
Preheat oven to 375ºF (190ºC). Lay both halves of the bread on an aluminum-foil lined baking sheet cut-side up.
Use a knife to spread the butter evenly over both sides of the bread then top with the mozzarella and Parmesan.
Bake until the cheese is melted and the top is lightly browned, about 12 to 15 minutes.