Combine 500g flour and 350g water in a large mixing bowl. Mix until a shaggy dough forms and no dry flour remains.

Cover the dough with a damp towel and let it rest for 1 hour. This helps hydrate the flour and develop gluten.

Add 100g active sourdough starter on top of the dough. Using your hands, mix it thoroughly, pinching and folding until the starter is fully incorporated.

Cover and let the dough rest for 30 minutes.

Sprinkle 10g of salt over the dough. Mix by squeezing the dough between your fingers and folding it over itself until the salt is fully combined.

Cover the bowl with plastic wrap or a damp kitchen towel and let the dough rest for another 30 minutes.

Perform 4 rounds of stretch and folds, spaced 30 minutes apart.

Let the dough rise at room temperature until it increases by 70% in volume (about 4–6 hours). The dough should look puffy, with bubbles visible on the surface.

Turn out the dough onto a lightly floured surface and gently stretch it into a square. Spread 100g olives and 5g chopped rosemary evenly over the surface. Fold the dough like an envelope (side to center, then roll it up like a burrito).

Shape it into a boule (round) or batard (oval). Place it seam side down in a floured banneton or a bowl lined with a floured kitchen towel.

Cover and refrigerate for an overnight cold proof (8–12 hours).

Preheat your oven to 475°F with a Dutch oven inside for at least 30 minutes.

Turn the shaped dough out onto a piece of parchment paper and score the top with a sharp razor blade, sharp knife, or lame.

Carefully place the dough into the hot Dutch oven, cover, and bake for 20 minutes.

Remove the lid, reduce the oven temperature to 450°F, and bake for another 20–25 minutes until it has a deep golden crust.

Let the olive sourdough bread cool completely on a wire rack before slicing.