Whisk together water and yeast in a large bowl; let sit until yeast is foamy, about 10 minutes. Add flour, and stir with a fork until dough forms and all flour is absorbed; let dough sit to allow flour to hydrate, about 20 minutes. Add salt, then transfer dough to a lightly floured work surface, and knead until smooth and elastic, about 10 minutes. Transfer dough ball to a lightly greased bowl, cover bowl with plastic wrap, and place bowl in a cold oven or microwave. Let dough rest until doubled in size, about 45 minutes.
Transfer dough to a lightly floured work surface, and shape into an 8-inch x 6-inch rectangle. Fold the 8-inch sides toward the middle, then fold the shorter sides toward the center, like a T-shirt. Return dough, seam side down, to the bowl. Cover with plastic again, and return to oven. Let sit until doubled in size, about 1 hour.
Remove bowl with dough from oven, and place a cast–iron skillet on the bottom rack of oven; position another rack above skillet, and place a baking stone or upside down or rimless sheet pan on it.
Heat oven to 475° F. Transfer dough to a lightly floured work surface, and cut into three equal pieces; shape each piece into a 14-inch rope. Flour a sheet of parchment paper on a rimless baking sheet; place ropes, evenly spaced, on paper. Lift paper between ropes to form pleats; place two tightly rolled kitchen towels under long edges of paper, creating supports for the loaves. Cover loosely with plastic wrap; let sit until it doubles in size, about 50 minutes.
Uncover; remove towels, and flatten paper to space out loaves. Using a sharp razor, knife, bread lame, or scissors, slash the top of each baguette at a 30–degree angle in four spots; each slash should be about 4 inches long. Pull out the oven rack with the stone or baking sheet on it and, using the corner of the parchment paper as a guide, slide the loaves, still on the parchment paper, onto the baking stone or pan. Place ice cubes in skillet (this produces steam that lets the loaves rise fully before a crust forms). Bake the baguettes until darkly browned and crisp, 20 to 30 minutes; cool before serving.