Start by measuring/weighing the tepid water into a bowl. Next measure/weigh the active sourdough starter and add to the water. At this point your sourdough starter should float on top of the water. This is an excellent sign that your starter is active enough to make this recipe. Whisk the starter and water. Next, weigh the flour into the bowl, and weigh salt on top of the flour. Using a spatula to mix, until a soft and hydrated dough forms. Turn onto a board or counter top and let autolyse (rest) for 15-30 minutes.
After the dough has rested on the counter, it should be soft. You can begin to chop it up with your bench scraper, slap it, and knead it for about 10 minutes. Give it a few minutes of rest and then begin kneading it again for another 10 minutes. You will continue kneading until the dough looks smooth and passes the window pane test.
After your dough is properly kneaded, shape into a tight ball and place the dough back into the bowl with a lid to rise at a temperature no higher than 75℉. You want it to rise to 3 ½ it's original volume or bulk. It will be about 3 cups of unrisen dough and rise to about 10 ½ cups.
After the first rise, with lightly floured hands turn the dough onto a floured board or countertop. Deflating it and then reshaping into a tight ball. Place back into the bowl. Cover and let it rise again.
Form and shape the loaves. You will start by weighing (approx. 855 grams) the dough. Divide into three equal pieces, each weighing approx. 285 grams.
Pat each piece of dough flat into a small rectangle-like shape. Then, fold the bottom half into the middle, and pat down again. Then fold the top half into the middle, and pat down.
Taking the palm of your hand make a trench across the middle of your dough, and then again fold the top half into the middle. Pressing your palm along the side to pinch the crease closed.
Placing your hands flat, one on top of the other in the middle of the dough, begin to roll the dough moving your hands in opposite directions, outwards to the end of the dough. Tapering the ends if you'd like. Quickly and confidently transfer each shaped baguette to a floured tea towel or cloche. Keeping the baguettes close to each other without touching. Cover and let rise again until almost tripled in size about 1 hour depending on environmental factors. They should look nice and supple to the touch when they are ready. While you wait for the final rise, preheat the oven to 500℉ Add a cast iron skillet filled with water, to the bottom rack of the oven. Gently but quickly flip your loaves, one at time, onto a floured sheet pan or baguette mold, seam-side down. If you are using a pizza stone, you will slide the baguettes off the sheet pan directly onto the pizza stone. If you are going to do that, lay your baguettes on an upside down floured sheet pan, so they can slide right off into the oven on the pizza stone.
At the very last minute before putting them in the oven, lightly flour the surface of your dough and cut three deep slashes with a razor or lame: Start on the left side with a 45° angle cut. Another 45° angle cut that goes slightly by the first slash. The last cut on the right side will go slightly past the second cut at another 45° angle.
Spray with water and quickly get the pan into the oven, or slide the baguettes on the hot pizza stone. Turn the oven down to 475° After 15 minutes, take the cast iron skillet filled with water out of the oven. Let your baguettes bake for an additional 15 minutes until perfectly golden brown. Transfer to a cooling rack.
Don't get discouraged, just keep practicing!