Cake serves 60. Each cookie serves 1.
Bake your favorite 2-layer cake recipe or mix in sheet pan. Cool cake in pan on wire rack 10-15 minutes. Remove from pan and cool completely. Place on foil-wrapped cake board.
Make Roll-Out Cookie recipe or use refrigerated cookie dough. Roll out to 1/8-in thickness; cut cookies using locomotive engine and airplane. With knife, cut out tree and train car cookies using patterns. Bake 7-10 minutes or until golden brown.
Spatula ice locomotive engine, train cars and airplane; add candy decoration accents. Decorate tree cookies with brown tip #47 outline trunks and green tip #352 leaves.
Spatula ice cake sides with white buttercream icing. Spatula ice top of cake with green buttercream icing "grass" and blue buttercream icing "sky". Pipe tip #47 brown icing train tracks; position locomotive, train car and tree cookies on cake top. Place airplane cookie on cake. Pipe tip #1D white banner; add tip #2 message. Using fingers, flatten marshmallows; arrange in groups on cake top to form clouds. Add tip #14 shell top border and tip #16 shell bottom border.