In a large bowl, mix together the flour, water, and sourdough starter until no dry flour remains. Cover and let rest for 30–45 minutes (autolyse).

Add salt and mix by hand or with a dough whisk until incorporated.

Perform 3 sets of stretch and folds over 3–4 hours during bulk fermentation, keeping the dough covered in between.

Once the dough has risen about 50% and feels airy, cover tightly and place in the refrigerator overnight (cold proof).

The next morning, gently divide the dough into 3 equal portions. Preshape each into a loose log and rest for 10–15 minutes.

Shape each piece into a baguette and place seam side down on a baguette pan or floured couche.

Cover and proof for 1 hour at room temperature, until slightly puffy.

Preheat the oven to 475°F (245°C) with a baking stone or steel inside.

Score each baguette with a sharp blade or lame, and load onto the hot stone or tray.

Bake with steam (add hot water to a tray or mist oven walls) for 10 minutes, then vent steam and continue baking for 10–15 minutes more, until golden brown.

Cool completely on a wire rack before slicing.