From this snowy corner of our world, I have a suggestion for a mold
to produce something more platter-like - a snow disk. I've had students use
these with success - just as has been suggested, the interior (or
exterior-depending on the side you choose to use) gets covered with
newspaper, paper towelling or some such to aid in releasing. Course, it's
warming up around here enough to sled, so now we're gonna have to pry those
disks out of the kids hands!
Stay warm, or cool, whereever you are!