The dough that goes hard and you can make Christmas decorations out of

[Frayedknot]

Anyone?

Salt!

salt dough

try tis

Salt and...

I'm guessing flour, water...anything else vital?

Lots of salt. Otherwise it goes mouldy.

Great link, thanks AM!

Here is the basic recipe:
one cup of fine salt

one cup of flour

about half a cup of water