In a large bowl, mix together the cornmeal, strong flour, salt and yeast.
Gradually, pour the warm water into the bowl and combine to form a sticky dough. You may not need to use all of the water.
Spread some spare flour on your hands to prevent the dough sticking and roll the dough into a ball.
Place this round ball of dough in a clean bowl and cover with a damp cloth. Leave the bowl in a warm place and allow the dough to rise for around 1 hour, or until the dough ball has doubled in size.
Sprinkle flour on your hands and on your worktop. Remove the dough from the bowl, place it on the counter and punch it to deflate.
Roll it again to form another ball shape.
Place the dough on an oiled baking tray and sprinkle with flour.
Cover with a new cloth and leave in a warm place for a second proof, for 30 minutes, or until the dough has doubled in size.
Place the tray in a preheated oven at 500 F for 40 minutes, until golden brown.
Allow to cool for at least 30 minutes before cutting.