In a large bowl, whisk together all the ingredients until the poolish is smooth. Cover the bowl with a damp cloth and let rise in a warm place for about 2 hours or until it has doubled in volume.
Gently pour the warm water down the side of the bowl containing the poolish. Add the flour, salt and yeast. Blend well with your hands or a wooden spoon. Place the dough on a lightly floured work surface and knead for 1 minute. Form a ball and place in a clean lightly oiled bowl. Cover the dough with a damp cloth and let stand at room temperature for 20 minutes.
Give the dough a little flap, that is to say, stretch the dough slightly to be able to fold into 4. Put the dough back into the bowl. Cover with a damp cloth and let stand for another 20 minutes. Repeat two more times and let rise for 2 hours in a bowl covered with a damp cloth.
Place the dough on lightly floured work surface and divide into 4 or 6 even pieces. Without too much handling, shape each piece into an oval shape. Cover with a damp cloth and let rise for 20 minutes.
Line two baking sheets with parchment paper.
Take one piece of dough at a time and place on lightly floured work surface. Wrap the dough over itself while lengthening it to obtain a 38-cm (15-inch) long baguette. Repeat with the other pieces and place 2-3 baguettes per baking sheet, leaving 8-cm (3-inch) of space between each. Cover with a damp cloth and place the baking sheet in a warm place for 1 hour to 1 hour and 30 minutes.
With the rack in the middle position, place a cast iron skillet on the oven floor.
Preheat the oven to 250 °C (500 °F).
With a razor blade, make diagonal incisions on the surface of the baguettes.
Pour 125 ml (1/2 cup) of warm water in the skillet to humidify the oven. Immediately place a baking sheet in the oven and bake for 15 to 20 minutes, taking care to remove the skillet 5 minutes before the end of baking.
Put the skillet back in the oven with hot water and bake the other baguettes in the same way.
Cool on a rack so that the bread can cool off on all sides.