Combine 250 g of the water with the sourdough starter in a large mixing bowl and stir thoroughly. Incorporate the flour, mixing until no dry bits remain. Cover the bowl and let it rest for one hour. Meanwhile, dissolve the salt in the remaining 30 g of water.

Introduce the salted water to the dough and knead gently until the mixture becomes smooth and elastic. Perform a stretch and fold by lifting one edge of the dough and folding it over itself, rotating the bowl as you continue around. After this process, shape the dough into a ball and transfer it to a lightly greased bowl, covering with a damp cloth. Let it rest for another hour.

Repeat the stretch-and-fold process two additional times, each followed by a one-hour rest. Following the third set, allow the dough to undergo bulk fermentation for two hours, remaining covered throughout.

Turn the dough out onto a lightly floured surface and divide into four portions for smaller baguettes or two if you prefer longer loaves. Lightly flatten each piece, expelling excess air, and shape into rectangles. Fold the top edge down, applying downward tension with your thumbs. Continue rolling to form a tight cylinder. Seal the seam by pressing with your palm and pinching with your fingers. Roll the dough from the center outward to taper the ends.

Prepare a baking sheet with a couche or thick linen cloth floured generously with a blend of semolina and bread or rice flour. Nestle the baguettes seam-side up between the folds. Sprinkle with additional flour mixture and cover with plastic wrap or an inverted tray. Refrigerate to proof for at least 18 hours and up to 36.

If necessary, allow baguettes to come to room temperature to finish proofing. Preheat the oven to 250°C (480°F), placing a container of boiling water at the base to generate steam. Heat a baking stone or tray in the oven. Dust the hot surface with semolina. Invert the baguettes seam-side down onto it. Score each with a blade at a 30–45° angle to a depth of about 1.5 cm.

Bake for 30 minutes, rotating the tray and reducing the heat to 220°C (428°F) at the 15-minute mark. Once golden and crusty, remove the loaves and cool before slicing. Serve warm with butter or your preferred accompaniment.