01 - Combine bread flour and lukewarm water in a large bowl until just mixed. Cover and let rest for 30 to 45 minutes.
02 - Incorporate the active sourdough starter and fine sea salt into the dough. Mix thoroughly until a shaggy dough forms.
03 - Transfer dough to a lightly floured surface and knead or perform stretch and fold technique for 5 to 8 minutes until smooth and elastic.
04 - Place the dough in a lightly oiled bowl, cover, and ferment at room temperature for 4 to 6 hours. Perform stretch-and-folds every 30 minutes during the first 2 hours.
05 - Turn the fermented dough onto a surface, divide into two equal portions, and shape each into a tight round loaf.
06 - Place each loaf seam-side up in a floured proofing basket or bowl, cover, and refrigerate for 4 to 8 hours or proof at room temperature for 1 to 2 hours until puffy.
07 - Preheat oven to 450°F with a Dutch oven or baking stone inside.
08 - Place each loaf onto parchment paper, score the top, and carefully transfer it to the preheated Dutch oven or baking stone.
09 - Bake covered for 20 minutes, then uncover and bake for an additional 20 minutes until the crust is deep golden brown.
10 - Remove loaves and cool completely on a wire rack.
11 - Slice off the top of each loaf and hollow out the center, leaving a ¾ to 1 inch thick wall to hold fillings.