One point here is that you can boil water over a fire in a flammable container.

Here, this isn't about boiling, but similar: "Because the Neanderthals had no pots, we presume that they soaked their seeds in a fold of an animal skin," says Chris Hunt, a genuine (checks) expert in cultural paleoecology.

https://archaeologymag.com/2022/11/neanderthals-cooked-surpr...