Remove cake from pans and peel off parchment. Brush each layer with the simple syrup. Arrange one layer on a serving plate and spread with approximately 1/4 of icing. Top with another layer and repeat with icing and top with the remaining cake layer. Ice the top, reserving a small amount of icing to fill in the layer sides. Run a bench scraper or long straight edge spatula around the outside of the cake to smear and flatten the icing into a "naked cake" look. Dust the top with cinnamon and cut into desired wedges.