Roughly 4-8 hours before starting the dough, feed your sourdough starter by adding equal parts (by weight) water and all-purpose flour to your already active starter. I like to do 50 grams of water and 50 grams of flour.
Once the starter has been properly fed, let it sit at room temperature until it doubles in size. This will vary in time based on the temperature of your kitchen.
When the starter has doubled and is at its peak rise, measure out 125 grams of ripe starter.
Add the starter to a mixing bowl and combine it with 287 grams of cool water (filtered or tap is fine). Use a fork or whisk to combine until you have a milky-looking liquid with no clumps.
In a separate mixing bowl, add 337 grams of bread flour.
To that, add ½ teaspoon of fine sea salt or table salt and ¾ teaspoon white sugar. Mix well.
Pour the starter and water mixture into the flour mixture.
Use a fork to whisk together, avoiding clumps if possible.
Mix until you achieve a sticky, wet dough mixture.
Cover the bowl with a damp kitchen towel. Let it rest until the dough has doubled in size, 10-18 hours.
Tip: If you need to rest it for a longer time, wait until the dough has nearly doubled in size, then place in the refrigerator with a towel on top for 12-24 hours.
After the dough has doubled in size, generously dust a work surface with flour. Carefully remove it from the bowl and place it on a clean, lightly-floured surface. Be sure that the dough comes out of the bowl in one piece.
Next, grab one corner over of the dough and stretch it upwards, then fold it into the center of the dough. Repeat this with each corner multiple times until the dough becomes less stretchy and more resistant to the pulls.
The dough should roughly resemble a slightly smaller, flattened sphere.
Grab a large mixing bowl or a tall, straight-sided vessel and brush the insides of the bowl with a few tablespoons of olive oil.
Gently place the dough, seam side down into the bowl.
Brush the top of the dough with more olive oil and a pinch of flake salt or coarse kosher salt.
Cover the bowl with a damp towel. Place in a warm draft-free spot to rise for 3 to 4 hours.
The dough is ready when it has doubled in size once again. If you gently poke it with your finger, it should hold the impression. If it springs back, let it rise for another 15 minutes.
Pre-heat the oven to 500º Fahrenheit.
Coat a sheet pan with roughly ¼ cup of olive oil. Dump the dough out of the bowl and onto the sheet pan. It will flatten slightly.
Use a bench scraper or a non-serrated knife to divide the dough into 2, 3, or 4 pieces.
Use your hands to take each piece and stretch it out into a long, even-thickness, baguette-like shape. 2 pieces will yield the longest shapes, 4 will be the shortest shape.
Generously sprinkle the tops of the baguettes with the flaky salt.
Place in the 500ºF oven and bake for 12-15 minutes, until golden on the tops and cooked all the way through.
Remove from the oven when done and allow to cool at least 5-10 minutes before slicing. Enjoy with butter, olive oil, jam, or as sandwich bread!