In a large bowl, dissolve the yeast in the warm water (see Notes). Using a rubber spatula, stir in 525g flour and the salt to form a soft, sticky dough. Do not knead. Cover with lightly greased cling film and let it rise at room temperature for 1 hour.
Stir down the dough (it will be sticky). Turn it onto a floured surface and with floured hands pat it into a 22cm square. Fold the square into thirds, forming a 22cm x 7cm rectangle. Fold the rectangle into thirds, forming a 7cm square. Place it in a large greased bowl, turning once to grease the top. Cover again and let it rise at room temperature until almost doubled, about 1 hour.
Punch down the dough and repeat the folding process. Return the dough to the bowl; refrigerate, covered, overnight.
Grease the bottom of a disposable foil roasting pan (see Notes) with sides at least 8cm; dust the pan with the polenta. Turn the dough onto a floured surface. Knead gently 6 to 8 times, then shape into a 15cm round or 20 to 25cm rectangle loaf. Place it into the prepared pan and dust the top with the remaining 1 tbsp of flour. Cover the pan with lightly greased cling film and let it rise at room temperature until the dough expands, about 1 hour 15 minutes.
Preheat the oven to 260C. Using a sharp knife, make 1 slash across top of the loaf if you make it a round one, or 3 slashes if you make it a rectangle shape. Cover the pan tightly with tin foil. Bake the loaf on the lowest oven shelf for 25 minutes.
Reduce the oven setting to 230C. Remove the foil and bake the bread until it is a deep golden brown, 25 to 30 minutes. Remove the loaf to a wire rack to cool.