Bake and cool book cake. Ice top and sides of cake smooth with buttercream. Cover top of cake with fondant. Comb sides of cake with small-tooth side of decorating comb. Grate chalk through a tea strainer and use decorating brush to apply chalk around top border of pages. Cut hidden dowel rods to 2 3/4 in. and insert in book cake to support 6 in. cake board holding castle. Position turret towers around cake and attach with icing. Pipe tip 4 door and doorknobs with pink royal icing. Tint 8 oz. of fondant green, roll into assorted-sized balls and position around bottom of castle. Position castle on cake. Attach turret towers with icing. Pipe tip 2 vines around edge of cake and position flowers. Write tip 2 violet message. Pipe tip 6 bead bottom border.
*Note: Combine Rose and Violet for violet shown. Combine Brown and Red-Red for brown shown.