Place the active sourdough starter and water in a large bowl.
Whisk together until well combined and the water turns tan and cloudy.
Add the all-purpose flour and bread flour. Use a spoon to combine until the dough is a sticky mass.
Sprinkle it with salt, and gently pinch it with your fingers. Cover and let rest for 1 hour.
After an hour, with wet hands complete 4 sets of "stretch and folds" in 30 minute intervals.
After the stretch and folds, cover, and refrigerate for 8 hours. When ready to work again, bring to room temperature for at least an hour.
Transfer the dough to an unfloured work surface, dust it with flour then twist the it into a ball. Let it rest for 20 minutes.
Wet a bench scraper and gently wedge it under the dough. Transfer the dough to a cloth lined banneton that's been sprinkled with rice flour.
Cover the bowl, transfer it to the refrigerator, and allow the dough to rest until it doubles in size.
Transfer the dough to parchment paper and bake in a preheated Dutch oven covered at 450°F for 30 minutes, then uncover for an additional 15 minutes.
Allow the bread to rest until cooled completely before slicing. Store in a plastic bag for 2 days to keep bread fresh.
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