In a large bowl, combine 3 cups flour and the salt. Make a well in the center, pour in the yeast mixture and stir with a wooden spoon; the dough will feel sticky and elastic. Transfer to a floured work surface and dust with some of the remaining flour. Knead for 7 to 8 minutes, adding flour a little at a time as necessary until the dough is smooth and springy. Wash and dry the bowl, then lightly grease with oil. Return the dough to the bowl, cover tightly with plastic wrap and let rise until doubled, 1 to 1½ hours.