In a large mixing bowl, combine active sourdough starter and warm water. Stir until well mixed and slightly foamy.

Add flour and salt to the bowl. Mix with a wooden spoon or your hands until a shaggy dough forms. Cover with damp kitchen towel and let rest 30 minutes.

Perform first stretch and fold: wet your hands, grab one side of dough, stretch up and fold over to opposite side. Rotate bowl 90 degrees and repeat 3 more times. Cover and rest 30 minutes.

Repeat stretch and fold process 3 more times, resting 30 minutes between each set. Dough will become smoother and more elastic.

After final fold, cover tightly and let rise at room temperature 4-6 hours until doubled in size, or refrigerate up to 5 days.

Turn dough onto floured surface and divide in half. Shape each portion into a round loaf, creating surface tension by tucking edges under.

Place seam-side up in banneton baskets or bowls lined with floured kitchen towels. Cover and proof 2-4 hours at room temperature, or overnight in refrigerator.

Preheat Dutch oven and lid to 450°F for 45 minutes. Carefully turn one loaf onto parchment paper, score top with sharp knife.

Lower bread into hot pot using parchment paper. Cover and bake 20 minutes, then remove lid and bake 20-25 minutes until deep golden brown.

Remove from pot and cool on wire rack at least 1 hour before slicing. Repeat with second loaf or refrigerate for later baking.