Yes, this is the black forest cake that was promised as a reward on the Portal video game and no, you can't eat it. "The cake is a lie" is a phrase popularized by the Portal game and can be seen scribbled around on the backstage areas of the Aperture Science Laboratories. The cake was used by GLaDOS as a motivating perk for solving the intricate puzzles on the laboratory. This cake papercraft is from designer Mike McDermott, check it out.
Portal Papercraft - Cake [billybob884]