There is an article on Native American Cooking Tools that mentions early clay cooking pots, ( not how to water proof them)
and boiling in hides hung near fires here:: www.journalofantiques.com/Aug02/hearthaug02.htm

I believe the Ojibwe cooked in a pots made of birch bark. As long as the flame doesn't touch the pot, liquids can be boiled in birch bark.