That pottery is not a prerequisite for plant food preparation is
demonstrated currently in  Ethiopia, for instance. As I have observed,
pottery in a home in the Highlands may be confined to a single water jar
(indeed often even this has been replaced by a plastic jerry can). Ground
grains (teff preferably, but also sorghum, wheat, pulses etc) are mixed
with water and fermented in a container (basketry, stone, gourd, wood,
skin.... will do), the resultant  batter is baked on a hot plate (flat
surface of stone or clay) over a fire, to make the bread "injera". The
toxic seeds of grasspea are detoxified by being soaked in hot water (again
any container will do), dried, roasted (hot plate as before) and hulled,
ground, spiced, mixed to a paste with water and used as a sauce - no pots.
Water, of course, may be heated in many containers other than pots, on or
off the heat source.

In many societies worldwide, pulses (esp. chickpea) and other grains are
prepared by short roasting over a fire, not only as snack food or as
rations for travelling, but also as a staple.

Cheers, Ann