We did this a lot a few years ago. If you google paper casting, there's lots of info with different recipes. Altough it's called paper casting, cotton fiber is always used as a binder. You can use ceramic cookie molds/stamps or decorative shortbread pans from Rycraft, Brown Bag or Pampered Chef
http://www.cookiestamp.com/
http://www.brownbagcookiemolds.com/
You can spray the molds with Pam to make the casting release. Use a paper towel to soak up excess spray first.
A couple of notes of caution, it is really fun, but messy! A great outdoor activity, if you do it indoors, have lots of towels!
Leaving them on a cooling rack on the counter overnight will also usually dry them. But if you want to reuse the mold right away, CAREFULLY dry them in a microwave. Like try 10 or 20 seconds, and the mold will be extremely hot, so use one of your home made quilted potholders!!