Whip heavy cream with sugar, mace, nutmeg, and cinnamon. On a long plate, spread one side of a chocolate wafer with whipped cream; stick next wafer to it. Add whipped cream to other side; add another chocolate wafer. Continue layering until you have one long log of wafers held together with whipped cream. Frost log with remaining whipped cream. Sprinkle with grated chocolate or cinnamon. Freeze 1 to 2 hours. Slice diagonally and serve.
Note: If log will be in freezer longer than 2 hours, loosely wrap plate in foil taking care not to let foil touch sides of log. Remove from freezer and leave at room temperature 5 minutes before slicing.