In a large mixing bowl, whip the cream and sugar until it starts to form peaks (Tip: don't over beat it...it will start turning into butter!). Gently fold in the Grand Marnier and cinnamon.
On the platter you plan to serve the cake on, start assembling your cake by adding a large spoonful of whip cream to each wafer and stacking them on their edges to form a long log, making sure you have some whip cream left over to cover the outside!
Cover the rest of the cake with the remaining whip cream then refrigerate for at least 6 hours. Using a peeler, shave the bar of chocolate over top of the cake before serving.
Cut into the cake so that you can see the layers (so perpendicular or at a 45 degree angle to the direction of the wafers).