Using an electric mixer, beat the butter, Parmesan, mozzarella, garlic powder, parsley, pepper and salt on medium speed until smooth and fluffy.
Spread the butter-garlic mixture evenly over each half of the French bread.
Wrap the bread tightly in foil and bake for 10 minutes. Open the foil and lay the bread cut-side-up on the foil and bake for an additional 5 to 10 minutes, until the bread is golden brown. Slice and serve immediately. Leftover bread should be stored in a zip-top bag in the refrigerator for up to 2 days.