If using dry yeast, Measure the flour into a bowl and make a well in it. Sprinkle in the yeast and pour 100 g water on it. Leave for 15 minutes. Add the rest of the water and add the salt. Mix the ingredients together and turn out onto the counter and knead for 10 minutes.
Measure the flour, water, salt, and yeast into a bowl. Mix the ingredients together and turn out onto the counter and knead for 10 minutes.
Cover and let rest for 15 minutes before folding in the onion and the celery. Cover again and let rest for 90 minutes.
Turn out the dough on to the counter and shape into one or two tight balls. Line one or two rising baskets with the celery leaves and pop the ball(s) into the basket(s). If you don't have baskets you can use shallow bowls or collanders lined with celery leaves. Cover and let rise 60 minutes. Pre heat the oven to 230 degrees.
Invert the dough out of the baskets/bowls onto baking trays lined with non stick baking parchment or coarse polenta/semolina. Pop the dough in the oven and bake for 10 minutes at 230. Turn the oven down to 200 and bake for a further 30 minutes.
Let it cool completely before eating. This bread is particularly good with strong cheese.