First, make the cupcakes. They can be any flavor. When they are cooled, frost them with your preferred color of frosting. I chose white.
Then, draw the outline of the arc reactor on them.
Then, fill them in with a light blue frosting, most likely out of a tube.
There you have it! I did "3" cupcakes as well, in honor of Iron Man 3 coming out on May 3rd.