Heat the oven to 400°F.
In a small skillet, heat the oil over medium heat. Add the garlic, salt, and pepper and cook, sizzling gently for about 2 minutes, stirring occasionally. The garlic should soften and become fragrant but not brown. Put the butter in a small bowl and pour the oil and garlic over it. Blend until smooth enough to spread evenly.
Make diagonal slices in the bread at 3/4-inch intervals, stopping short of the bottom crust. Slather some of the garlic butter into each cut. Slip the loaf back into the paper bag that it came in (or use a torn paper grocery bag; avoid those with printing or plastic on them). Wet the entire bag with a spray bottle or a very fast pass under the faucet. Pop the package into the oven and bake until it smells of popcorn and the crust is crisp, 10-15 minutes.
For herbed garlic bread, add 1/4 cup chopped fresh flat-leaf parsley or 2 Tbs. chopped fresh thyme, oregano, chives, or basil to the butter along with the garlic.