Combine sourdough starter, bread flour, and 325g water in a large bowl. Mix until no dry flour remains. Cover and rest for 30 minutes.
Add salt and remaining water, gently working them in with wet hands. Perform 4-5 stretch and folds in the bowl.
Cover the dough and rest for 30 minutes at room temperature (70-75°F).
Meanwhile, heat olive oil in a small pan over low heat. Add minced garlic and sauté for 2-3 minutes until fragrant but not browned. Cool completely.
Perform your first set of stretch and folds (grab dough, stretch up and fold over itself, rotate bowl 90° and repeat 3 more times).
Cover and rest for 30 minutes. Perform a second set of stretch and folds.
During the third set (30 minutes later), gently spread the cooled garlic and oil over the dough. Incorporate through the stretching and folding process.
Cover and allow to bulk ferment for 3-4 hours total from when you mixed in the salt. Dough should increase by about 50%.
Turn dough onto a lightly floured surface. Shape into a round by pulling edges toward the center. Let rest seam-side down for 20-30 minutes.
For final shaping, flip dough over, stretch into a rectangle, fold sides in like a letter, then roll from top down into a tight package.
Prepare a proofing basket by dusting with rice flour. Place shaped dough seam-side up in the basket.
Cover and refrigerate overnight (8-12 hours) for final proof.
Place Dutch oven in oven and preheat to 475°F for at least 45 minutes.
Remove dough from proofing basket onto parchment paper. Score the top with a sharp blade.
Using parchment as a sling, lower dough into preheated Dutch oven. Cover with lid and bake for 25 minutes.
Remove lid and continue baking 20-25 minutes until deep golden and internal temperature reaches at least 205°F.
Transfer to wire rack and cool completely (at least 2 hours) before slicing.
Notes
Your sourdough starter should be very active and bubbly before use – feed it 8-12 hours before making your dough.
The cold overnight proof develops flavor and makes the dough easier to handle.
For best results, use a kitchen scale to measure ingredients precisely.
Nutrition facts are estimates and may vary based on ingredients used, portion sizes, and preparation methods.