01 -
Preheat the oven to 400°F. Line a rimmed baking sheet with foil.
02 -
Cut the loaf in half lengthwise. Set both halves on the baking sheet with the cut sides facing up.
03 -
In a small bowl, stir together the softened butter, olive oil, minced garlic, salt, pepper, and 1 tablespoon parsley until evenly combined.
04 -
Spread the garlic butter over the cut sides of the bread, reaching the edges. Tent loosely with foil and bake for 10 minutes.
05 -
Uncover the bread. Sprinkle mozzarella evenly over both halves, then add Parmesan and red pepper flakes if using.
06 -
Return to the oven uncovered and bake for 6-8 minutes, until the cheese is melted and bubbling. Broil for 1 minute for deeper browning if desired.
07 -
Sprinkle with more parsley, rest for 2 minutes, then cut into 8 pieces and serve warm.