1. Prepare the Roasted Garlic: Preheat your oven to 400 F (200 C). Slice off the top quarter of the garlic head to expose the cloves. Drizzle with a little olive oil, wrap in foil, and roast for 30-40 minutes, or until the cloves are soft and golden brown. Let cool, then squeeze out the softened garlic paste.

2. Combine Starter and Water: In a large mixing bowl, combine the active sourdough starter with the warm water. Stir gently with a spatula or your hand until the starter is mostly dissolved and the mixture is milky.

3. Add Flour and Salt: Add the bread flour and fine sea salt to the starter mixture. Mix with your hand or a sturdy spatula until no dry flour remains and a shaggy dough forms. Cover the bowl with a damp cloth or plastic wrap and let it rest for 30 minutes (this is called autolyse).

4. Incorporate Garlic and Rosemary, Then Stretch and Fold: After the rest, add the roasted garlic paste and chopped fresh rosemary to the dough. Gently fold them in. Perform your first “stretch and fold” by grabbing a portion of the dough from one side, stretching it upwards, and folding it over to the center. Rotate the bowl a quarter turn and repeat this process 3-4 times until the dough tightens slightly. Cover and let rest for 30 minutes. Repeat this stretch and fold process 3-4 more times, every 30 minutes, for a total of 3-4 sets. The dough will become smoother and more elastic with each set.

5. Bulk Fermentation (First Rise): After the final stretch and fold, cover the bowl and let the dough bulk ferment at room temperature for 3-4 hours, or until it has increased in volume by about 30-50% and looks bubbly. The exact time will depend on your kitchen temperature.

6. Shape the Loaf: Gently turn the dough out onto a lightly floured surface. Shape it into a round or oval loaf. For a round loaf, gently pull the edges towards the center, then flip it over and use the tension of the counter to create a tight, smooth surface.

7. Proofing (Second Rise): Place the shaped dough seam-side up into a floured banneton basket or a bowl lined with a floured kitchen towel. Cover with plastic wrap and proof at room temperature for 1-2 hours, or for a deeper flavor and easier handling, place it in the refrigerator overnight (8-12 hours). The dough should feel puffy and slightly springy when gently poked.

8. Bake the Bread: Preheat your oven to 450 F (230 C) with a Dutch oven inside for at least 30 minutes. Carefully remove the hot Dutch oven, invert the dough into it, and score the top with a sharp knife or razor blade. Cover and bake for 25 minutes. Remove the lid and continue baking for another 15-20 minutes, or until the crust is deeply golden brown and the internal temperature reaches 200-210 F (93-99 C). Let the loaf cool completely on a wire rack before slicing.