In advance, make fondant trees and flags for cake sides. For trees, roll out primary green fondant 1/8 in. thick; cut triangles in various heights from 1 in. to 1½ in. high and from 1 in. to 1¼ in. wide. Cut slits for branches or use confectionery tool to pull fondant edges out to resemble branches; let dry until firm on cornstarch-dusted surface. For flags on cake sides, roll out primary yellow, blue and red.fondant 1/8 in. thick;cut flags and let dry on cornstarch-dusted surface.
Bake and cool your favorite 2-layer cake. Lightly ice in buttercream icing to prepare for fondant covering. Position cake on foil covered cake board. Roll out and cover cake with blue tinted rolled fondant; smooth.
Roll out green-tinted fondant 1/8 in. thick; cut wavy strips for hills in various heights from 1 to 2½ in. Attach 1 group of hills for background with damp brush; attach 2nd group for foreground. Add more strips as desired. Attach fondant flags and trees to cake with damp brush, trim flagpoles as needed. Draw holes with black FoodWriter. Cut out construction paper flags; write message with black FoodWriter. Tape flags to sticks and insert in cake top. Position topper.