- Melt 3 oz of chocolate and grate 4 oz of chocolate. Set aside.
- Follow the treasure chest cake recipe and make up the cake mixture and bake the cake. Cool it, cut off a piece about 1 by 1 1/2 inches to make engine shape from one end.
- Follow our butter icing recipe, and make icing, reserve 2 tbsp of it. Use yellow food color to color the remainder and properly cover the cake. Mix the melted chocolate with reserved butter icing.
- Fill up piping bag with mixture fitted with a writing nozzle, finally make features on the bus with nozzle. Make a smooth paste of icing sugar with water and pipe faces on smarties and arrange them in the windows of bus.
- Cut off the mini rolls into two, arrange rolls under the cake to resemble with wheels. Place on a board and fill the whole board with grated chocolate.