This is the salt dough recipe I did:

http://simplybeingmum.com/2013/03/18...-dough-recipe/

I don't think I added all the water it called for (I'm sure that's no help to you... Sorry). I baked them at 200 F for close to 3 hours, the thicker ones needed flipping. They didn't crack at all though.

I'm not sure how well it would work for handprints though, as I said I had to push their fingers in quite hard. It might work if you made them thicker and pushed quite deep, then cut them out after.