Spatula ice cake smooth with buttercream icing; let set about 15 minutes. Dip pattern press into cornstarch, then randomly imprint design on cake sides. Using buttercream, pipe tip 2 balls on imprinted areas. Add tip 5 bead bottom border. Pipe tip 12 mounds of icing at various heights on cake top; position roses on mounds. Pipe tip 352 leaves with green buttercream icing.