In a blender pulse butter and parsley until parsley is finely chopped. Season butter with salt and pepper. Parsley butter may be made 2 days ahead and chilled, covered. Bring butter to room temperature before proceeding.
Prepare grill.
Halve bread lengthwise and spread cut sides with parsley butter. On a rack set 5 to 6 inches over glowing coals grill bread, cut sides up, covered, 2 minutes, or until parsley butter melts into bread. Turn bread over and grill until just toasted, 1 to 2 minutes.
