Mix 250 grams of water with the sourdough starter in a bowl until fully combined. Add the flour and stir until no dry patches remain. Cover the bowl and let it rest at room temperature for 1 hour. Meanwhile, dissolve the salt in the remaining 30 grams of water.

Incorporate the saltwater into the rested dough, mixing thoroughly until it becomes smooth and cohesive. Stretch and fold the dough by lifting one edge and folding it over itself, working around the bowl. Shape it into a ball, place it in a lightly oiled bowl, and cover with a damp cloth. Let it rest for 1 hour.

Repeat the stretch and fold technique two more times at hourly intervals. After the third fold, let the dough bulk ferment for an additional 2 hours, keeping it covered.

Transfer the dough to a lightly floured work surface. Divide it into four equal portions for demi-baguettes, or two for full-sized baguettes. Gently degas each piece and shape into rectangles.

Starting from the top edge, roll the dough downward, applying pressure with your thumbs to create surface tension. Continue until a taut cylinder forms. Seal the seam by pressing with your palm, then pinch shut with your thumbs and forefingers. Roll each baguette from the center outward to form pointed ends.

Prepare a baking tray with a couche or thick linen cloth dusted with a 50/50 flour-semolina mix or rice flour. Lay the shaped baguettes seam-side up within the cloth folds. Dust with additional flour mixture and cover with plastic wrap or an inverted tray. Refrigerate for 18 to 36 hours.

If necessary, allow the baguettes to sit at room temperature to finish proofing. Preheat the oven to 250°C (480°F) and place a baking tray or stone inside to heat. Add a container of boiling water at the base of the oven for steam. Once the oven is ready, dust the tray with semolina, lay the baguettes seam-side down, and score them at a 30–45° angle to a depth of 1.5 cm.

Bake for 30 minutes, rotating the tray after 15 minutes and reducing the heat to 220°C (428°F). Once baked, cool the baguettes before slicing and serving.