To make the starter: Place 1/2 cup flour and 1/4 cup water in a coverable bowl; stir well. Cover and let sit at room temperature overnight. The next day, add 1/2 cup flour and 1/4 cup water to the bowl. Cover and let sit at room temperature overnight. On the third day, add 1/2 cup flour and 1/4 cup water to the bowl. Cover and let sit at room temperature overnight.
To make the dough: In a large bowl, dissolve the yeast and sugar in the warm water. Let stand until creamy, about 10 minutes.
Break the starter into small pieces and add it to the yeast mixture. Stir in 4 cups of flour and the salt. Stir in the remaining flour, 1/2 cup at a time, beating well after each addition. When the dough has pulled together, turn it out onto a lightly floured surface and knead until smooth and elastic, about 8 minutes. Sprinkle a little flour over the dough and then cover it with a dry cloth. Let it rise until double in size.
Put the dough back onto a lightly floured work surface and punch out the air. Divide the dough in half and knead each piece for 2 to 3 minutes. Shape each piece into a tight oval loaf. Roll and stretch into two loaves until they are approx 30cm diameter. Dust the tops of the loaves with flour. Cover with a dry cloth and let raise in a warm place until doubled in size. Meanwhile, preheat oven to 220 degrees C.
Bake in preheated oven for 30 to 40 minutes. Mist with water 3 times in the first 15 minutes. Loaves are done when their bottoms sound hollow when tapped. Let cool on wire racks before serving.