The Play button, immediately leading to another gate asking for the e-mail address, feels like a bait-and-switch (but I suppose that means I made it to stage two in the funnel).

How about combining the two screens into one?

  Design your dream cake,
  We bake and deliver to you!

  [_Email Address_______]

  (  Let's get started!  )

Otherwise, I like the idea for the drag-and-drop designer (and I can imagine a number of "assembled" foods where this model could apply: pizza, sandwiches, etc.).

Will there be a gallery to showcase other peoples' creations so I can order those, myself?

Happy Birthday, by the way!