In a large deep bowl, mix the flour and salt well.
In another bowl, dissolve the sugar and yeast in the water.
Add the yeast mixture and the sponge to the flour, and mix together.
Transfer the dough to a lightly floured surface and knead. If the dough sticks to your hands or the surface, add a little more flour as needed. Knead for about 10 minutes until the dough is smooth, then shape it into a ball.

Divide the dough into 4 equal portions. Stretch each portion slightly lengthwise and widthwise. At this point, add rosemary or olives if you like.
Fold the bottom and top edges toward the center and seal with your fingertips.
Stretch the dough again slightly, then fold the bottom and top edges toward the center and seal. Flip the baguette over and place it seam-side down on a baking sheet lightly greased with olive oil.

Cover with plastic wrap and let rise for about 1 hour.
Use a knife to make diagonal slashes on the bread.
Preheat the oven to 450°F (232°C).
Bake the bread for about 45 minutes.
While the baguettes are baking, you can mist them lightly with water.
Remove from the oven and let cool.

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