Combine the bread flour and water in a large bowl, stirring until no dry flour remains and you have a shaggy, sticky mass. Let this mixture rest for 30-60 minutes for autolyse.

Add your active sourdough starter and salt to the dough, then use wet hands to squeeze and fold the mixture until everything is fully incorporated, about 3-4 minutes.

Cover the bowl and let the dough rest at room temperature (70-75°F) for 4-5 hours for bulk fermentation. During the first 2 hours, perform a stretch and fold every 30 minutes: wet your hands, grab one side of the dough, stretch it up, and fold it over itself, then rotate the bowl 90 degrees and repeat until you've worked all four sides.

After the final fold, let the dough ferment undisturbed until it has increased in volume by about 50% and shows bubbles on the surface and sides.

Turn the dough out onto a lightly floured work surface and use a bench scraper to divide it into three equal pieces, each weighing about 320g. Gently pre-shape each piece into a loose rectangle by folding the sides toward the center, then let them rest uncovered for 20-30 minutes.

Take one piece of dough and gently press it into a rectangle about 8 inches long with the long side facing you. Fold the top third down to the center and press the seam with your fingertips to seal, then fold the bottom third up and over, sealing again to create a log shape.

Using both hands, roll the log back and forth with gentle, even pressure, starting from the center and working outward to elongate it to about 14-15 inches long. Repeat with remaining pieces.

Place the shaped baguettes seam-side up on a well-floured linen couche or kitchen towel, creating pleats between each one to keep them separated. Cover loosely with plastic wrap or another towel and let proof at room temperature for 2-3 hours, or refrigerate for 8-12 hours for a cold proof.

Place your baking stone or steel on the middle rack and a metal pan on the bottom rack of your oven, then preheat to 500°F for at least 45 minutes.

Cut a piece of parchment paper large enough to hold all three baguettes with a bit of space between them.

Carefully flip each baguette seam-side down onto the parchment paper, spacing them about 3 inches apart. Hold your blade or lame at a 30-45 degree angle to the surface and make one long, swift cut down the length of each baguette, about 1/4 inch deep, or create 3-4 diagonal slashes that slightly overlap.

Slide the parchment paper with the baguettes onto your preheated baking stone or a baking sheet, then quickly pour 1 cup of boiling water into the hot pan on the bottom rack and immediately close the oven door.

Bake for 10 minutes with the steam, then carefully remove the water pan and reduce the temperature to 450°F. Continue baking for another 12-15 minutes until the baguettes are deep golden brown and sound hollow when tapped on the bottom.

Transfer to a cooling rack and let cool for at least 20 minutes before slicing.