In a medium bowl, combine the lukewarm water and yeast. Stir to dissolve. Add the flour and mix until smooth, like thick pancake batter.

Cover with plastic wrap or a damp towel. Let ferment at room temperature for 2-3 hours until bubbly, puffy, and nearly tripled in size. Alternatively, refrigerate overnight (8-12 hours) for more flavor.

Add the remaining flour, water, yeast, sugar, salt, and oil (if using) to the sponge. Mix until a shaggy dough forms and no dry flour remains.

Kneading for 8-10 minutes by hand, or 6-8 minutes in a stand mixer on medium-low. The dough should be soft, smooth, slightly tacky, and elastic. It will pull away from the bowl sides cleanly.

Form dough into a smooth ball. Place in a lightly oiled bowl, turning to coat. Cover with plastic wrap or a damp towel. Proofing for 60-75 minutes at room temperature until doubled in size.

Turn dough onto a lightly floured surface. Using a bench scraper, divide into 3 equal portions (approximately 150g each).

Preshape each piece into a ball by tucking the edges underneath. Cover with a towel and let rest for 10-15 minutes (bench rest). This relaxes the gluten for easier final shaping.

Working with one piece at a time, press the dough gently into a rough rectangle about 4x6 inches. Keep the other pieces covered.

Fold the top long edge down to the center and press to seal with your fingertips. Fold the bottom edge up to meet it and seal again. You should have a tight log.

Using both hands, roll the log back and forth while applying gentle outward pressure. Form a torpedo shape 8-10 inches long, tapering the ends slightly. The baguette should have good surface tension.

Place shaped baguettes seam-side down on a parchment-lined baking sheet, spacing them 3-4 inches apart. Cover loosely with a damp towel or oiled plastic wrap.

Proofing for 45-60 minutes at room temperature until puffy but still slightly springy when gently pressed. They should not quite double, about 1.5x original size.

About 30 minutes before baking, preheat your oven to 450°F (230°C) with a metal pan on the bottom rack for steam. Optionally dust the baguettes lightly with flour.

Preheat oven to 450°F (230°C) for at least 30 minutes. Place a metal pan on the bottom rack for creating steam.

Using a sharp blade or lame, scoring each baguette with one long diagonal cut down the center (about ¼ inch deep) or 3 shorter diagonal slashes at a 45° angle.

Carefully pour 1 cup of hot water into the steam pan. Quickly slide the baking sheet with baguettes onto the middle rack. Close the oven door immediately to trap steam.

Bake for 18-22 minutes total. At the 8-minute mark, quickly open the door and mist the loaves with water for extra crust development. Continue baking until deep golden brown and the crust feels firm when tapped.

Transfer to a wire rack immediately. Let cool for at least 10-15 minutes before slicing. The crust will crackle as it cools. Best eaten within a few hours for maximum crispness.