Preheat oven to 350 degrees F.
Mince and mash garlic to a paste with salt using rounded end of a heavy knife. Stir together butter, oil, and garlic paste in a bowl until smooth, then stir in parsley.
Without cutting completely through bottom, cut bread diagonally into 1-inch thick slices with a serrated knife, then spread garlic butter between slices,
Wrap loaf in foil and bake in middle of oven 15 minutes. Open foil and bake 5 minutes more.
Cook's note: Bread can be spread with garlic butter 8 hours ahead and chilled, wrapped in foil. Let stand at room temperature 30 minutes before baking.
For a brighter flavor, you can substitute 1 tablespoon finely chopped fresh basil for 1 tablespoon of parsley.