You can make a wooden basin or waterproof pit. Fill it with water, drop in hot stones from a fire. This is common in preceramic cultures. https://en.wikipedia.o

You can make a wooden basin or waterproof pit. Fill it with water, drop in hot stones from a fire. This is common in preceramic cultures. https://en.wikipedia.org/wiki/Pot_boiler https://en.wikipedia.org/wiki/Pot_boiler -- https://en.wikipedia.org/wiki/Stone_boiling https://en.wikipedia.org/wiki/Stone_boiling