Roasting the garlic till it becomes sweet and jammy makes all the difference in this garlic bread preparation.
Preheat the oven to 275°F.
Trim the tips off the top of the garlic and put it in a small baking dish. Drizzle with the oil. Roast until it becomes soft, 30 minutes. Let it cool for 15 minutes.
Increase the oven temperature to 400°F. Line a baking sheet with parchment paper and set aside.
Squeeze the garlic cloves into a small bowl and discard the husk. Add the butter, salt, and the red pepper flakes and, using a rubber spatula, stir the mixture to form a paste.
Cut the bread lengthwise down the center. Spread the garlic butter generously on the cut sides and put them on the prepared baking sheet, cut side up.
Bake for 8 minutes, and then rotate the baking sheet 180 degrees. Bake until golden brown, 5 minutes. Let the garlic bread cool on the baking sheet for 5 minutes before serving.