Mailable Cake Postcard {Picture Tutorial &amp; Video Tutorial} ~ Awesome... Now you can surprise friends &amp; family with this three-dimensional, mailable postcard, cleverly disguised as cake. With only five ingredients in this crafty recipe — a large sponge, spray paint, caulk, spray adhesive and heavy paper — it&#39;s a piece of cake. Literally! Postage is around 3 dollars per slice, but the reaction from the recipient will be priceles! Great Tutorials!