In advance, ice 10 vanilla wafers smooth with light Kelly green icing. Use tip 233 and white icing to pipe Shaggy Mums on vanilla wafers; make extras to allow for breakage and let dry.
Bake and cool 2-layer cake. Use spatula and light Kelly Green icing to ice 8 x 4 in. cake smooth. Attach Shaggy Mums to cake top with icing. Use tip 18 and white icing to pipe shell bottom border. Use tip 18 and white icing to pipe rosette bottom border on top of shell border. Use tip 3 and white icing to pipe larger dots on top sides of cake; add smaller dots, gradually tapering in size halfway down side.
The rosette has the tight, swirling look of a rose, but is achieved in one continuous rotation, rather than with wrapped layers of petals. Single rosettes are also used as candleholders on top of a cupcake.