Using a cutting tool, make two diagonal cuts in the green dough to make a triangle shape for the bottom layer of the cake. Discard the side pieces.
Next, flatten a piece of red dough. Place the green dough over the red dough. Using the green dough as a guide, cut away the unwanted portions of the red dough.
Flatten a piece of white insulating dough. This should cover the cake shape as well as hang down the back of the stacked layers of cake. Place the cake on the flattened white dough as a guide. Cut away the unwanted portions of the insulating dough. Attach the remaining white dough to the back of the stack of colored dough.
With all the cake layers together, flip the layered stack over so that the white layer is now the top layer. Roll out three balls of dough and place them on the back corner of the cake.
Connect the LED by inserting the short terminal through the white dough into the blue layer of dough. Insert the long terminal into the green ball of dough.
Last, attach the battery holder. Insert the red wire into the colored cake layers through the back of the cake. Insert the black wire into the green ball. Next, turn on the battery holder to see the LED light up.