Wash the celery root well with a sponge. If there is lots of dirt on it you can peel it with a potato peeler.
Dry off any moisture on the celery and rub it with sea salt.
Wrap straw around the celery and then the clay so it is completely packed in.
Place the celery directly on the coals of a campfire and bake for 2-2½ hours. For an even result, turn it around a couple of times as it bakes.
Rake it from the coals, knock off the clay with the dull edge a large kitchen knife.
Remove the hay from the celery and cut it in large pieces, to be served with butter.