Mix the dough: In a large mixing bowl, combine 150 g sourdough starter, 310 g water, and 20 g olive oil. Stir to disperse the starter. Add 500 grams bread flour, 10 grams salt, and 2 tsp finely chopped fresh rosemary. Mix with your hands or a spatula until no dry flour remains and a shaggy, rough dough forms.Cover and let rest for 20–30 minutes. Perform the stretch and folds (round 1): With slightly damp hands, grab one side of the dough, gently stretch it upward, and fold it over itself. Rotate the bowl and repeat on all four sides. Cover and rest for 30–45 minutes.
Laminate the olives and feta: Scatter 120 g olives and 125 g feta evenly over the surface of the dough. Fold the dough over itself several times to fully enclose the add-ins. Cover the dough and rest for another 30–45 minutes.
Continue stretch and folds: Perform two more rounds of stretch and folds, spaced 30–45 minutes apart, just like the first round. By the final round, the dough should feel smoother, stronger, and more elastic and the olives and feta should be well distributed.
Bulk fermentation: Cover the dough and let it ferment at room temperature until it becomes puffy, aerated, and increased in volume by about 30–50%. This usually takes 3–6 hours total from the time of mixing, depending on the temperature of your kitchen. The dough should feel lighter and show bubbles along the sides and surface.
Shape the dough: Turn the dough out onto a lightly floured surface. Gently shape it into a round or oval by folding the edges toward the center, then flip it over and use your hands or a bench scraper to create tension across the surface.
Cold ferment overnight: Place the shaped dough seam-side up in a well-floured banneton or bowl lined with a floured towel. Cover and refrigerate overnight.
Preheat the oven: The next day, when you're ready to bake, place a Dutch oven with lid into the oven and preheat to 450° F.
Score and bake: Remove the dough from the fridge and gently invert it onto parchment paper. Score the top with a sharp blade or bread lame. Carefully transfer the dough into the preheated Dutch oven, cover with the lid, and bake for 20 minutes covered, then remove the lid and continue baking for another 18-25 minutes uncovered. The crust should be golden brown and the internal temperature of the bread should be 200 - 210° F.
Cool completely before slicing: Transfer the bread to a wire rack and let cool for at least 1 hour before slicing. This allows the crumb to fully set and prevents a gummy texture.