The famous butter cow is being unveiled on the state fairgrounds today.  But it won't be completely finished by the time it debuts at 2:30 this afternoon.  That's because fairgoers will get a chance to watch the sculptor, Sharon BuMann, finish the cow during the fair.  The butter cow has been around since the early 1920s and is one of the most popular exhibits at the fair.  It's made of more than 500 pounds of unsalted butter.  But all that butter won't go to waste once the fair is over.  Officials say it will be reused to create another sculpture.  The fair starts tonight and runs through August 19th.