About 1 hour before you anticipate your fed sourdough starter being at its peak activity, combine the 350 grams of warm filtered water and 500 grams of bread flour in a large mixing bowl. Stir with a dough whisk or your hands just until no dry flour remains and a shaggy dough forms. Cover the bowl with a damp cloth and allow it to sit undisturbed for 1 hour to autolyse.
After 1 hour add the mashed garlic, minced rosemary, 100 grams of active starter and 10 grams of salt to the dough.
Begin kneading the dough using a traditional slap-and-fold technique on a clean surface, or perform a focused, gentle kneading motion right inside the bowl. Continue working the dough for about 5 minutes, or until it starts to smooth out, pull away from the sides, and cleanly incorporate all the garlic and herbs. Cover with the damp cloth and let rest for 30 minutes in a warm spot.
The 15-Minute Intervals: After 30 minutes, perform your first stretch-and-fold. Grab one side of the dough, stretch it upward gently, and fold it over the center. Rotate the bowl 90 degrees and repeat until all four sides are folded. Cover and rest for 15 minutes. Repeat this stretch-and-fold process two more times at 15-minute intervals.
The 30-Minute Intervals: Once the short intervals are complete, perform another stretch-and-fold, cover, and let rest for 30 minutes. Repeat this process two more times at 30-minute intervals (for a total of three 30-minute cycles). You will notice the dough becoming smoother, shinier, and holding its shape much better with each set.
Bulk Fermentation & Shaping: Cover the dough with the damp cloth and let it sit undisturbed to bulk ferment at room temperature for several hours. The dough is ready to shape when it has roughly doubled in size, looks puffy, and shows a few air bubbles on the surface. (Note: This can take anywhere from 5 to 8 hours depending on the temperature of your kitchen).
Turn the fermented dough out onto a lightly floured surface. Gently shape it into a tight round boule.
Place the shaped dough seam-side down into a floured banneton basket, or into a bowl lined with parchment paper for effortless lifting later. Cover the basket with a plastic bag to lock in moisture and transfer it to the refrigerator to cold-retard overnight (aim for 12 to 14 hours).
Scoring and Baking: One hour before you are ready to bake, place your cast iron Dutch oven (with the lid on) into the oven and preheat it to 500°F for 1 hour.
When fully preheated, carefully remove the hot Dutch oven. If using the parchment paper method, gently lift the chilled dough out of the bowl by the edges of the paper, score the top deeply with a sharp lame or razor blade, and lower it directly into the hot pot. (If not using parchment, lightly flour the bottom of the hot pot, invert the dough directly into it from the banneton, and score).
Cover the Dutch oven with its hot lid and place it into the oven to bake covered for 25 minutes. After 25 minutes, carefully remove the lid from the Dutch oven. Bake uncovered for an additional 15 minutes, or until the crust is deeply browned and caramelized.
Carefully remove the bread from the pot and transfer it to a wire cooling rack. Allow the loaf to cool completely for at least 1 to 2 hours before slicing to let the interior crumb set perfectly. Enjoy!