Note: If your starter hasn't been fed you will need to do this prior to step 1. Be sure to read the notes under what is a sourdough starter. Also, it is highly recommended you use a kitchen scale, especially if this is your first loaf. Be sure to zero out the weight of the bowl.
Whisk together the active starter and the warm water in a large bowl. Add in the bread flour and sea salt. Mix until combined to form a rough dough. Cover with a damp towel and let rest for 30 minutes to an hour.
Step 2: Stretch and Fold the Dough
After your 30-minute rest is up it is time for the stretch and fold portion of making your sourdough bread.
Grab a corner of the dough and pull it up and towards the center. Repeat the process 4 or 5 times and let the dough rest again for another 30 minutes. You will repeat this folding process 4 different times over the next 2 hours.
Allow the dough to continue to rest in a warm place, ideally somewhere 68-70 degrees. It is ready when it has doubled in size (if it doesn't fully double that is okay). This can take as little as 3 hours and up to 12 hours depending on your environment, starter, etc. On average it takes about 8 to 10.
Step 3: Cut and Shape the Dough
Create two work surfaces, one for cutting (lightly floured) and the other for shaping.
Remove the dough from the bowl and place it onto your floured cutting work surface. Once it has settled down to the surface cut the dough in half if you want to make two loaves of bread from your dough. If not you can leave it whole and move on to shaping.
Use a bench scraper to move your dough over to your shaping surface. Fold the dough toward the center, turn and continue folding the dough toward the center.
Flip the dough over and gently shape it into a ball using a turning circular motion.
Step 4: Let the Dough Rest Again
The dough needs to rise again but lucky for you not nearly as long as the previous time.
Place your dough in a bowl (covered with a damp cloth) to sit and rise for another 30 minutes to an hour in the fridge. Allowing the dough to sit in the refrigerator during the second rise will make the bread firm up and make it easier for the next step, which is scoring the dough. The dough will be ready when it just slightly begins to puff up.
Right before the dough is finished with the second rise preheat your oven to 450 degrees.
Step 5: Score the Dough
Line your Dutch oven with some parchment paper and place the dough inside.
Before your bread goes into the oven, score your dough about 2 inches in the center of the dough.
Step 6: Bake the Dough
Place your dough in the oven (center rack, lid on) and allow it to back for approximately 30 minutes.
After the 30 minutes have passed, reduce the temperature to 400 degrees, uncover the dutch oven and bake for additional 20 minutes or until your bread has a golden brown color.
Although it is tempted to want to taste your bread right out of the oven, allow it to cool on a wire rack for 1 hour before slicing. Cutting it too soon could risk you having a gummy inside.