Mix starter, water, flour, and salt in a large mixing bowl by hand until a shaggy dough forms. There should be no overly wet or dry spots in the dough.
Cover and rest for 1 hour.
Perform 1 set of stretch and folds (instructions below). Cover and rest for 30 minutes.
Sprinkle olives and rosemary across the top of the bread dough. Perform second set of stretch and folds. Cover and rest for 30 minutes.
Perform 4 more sets of stretch and folds with 30 minute rest between sets.
After the 6th set of stretch and folds, rest the dough for 2-3 hours until it’s grown by ~ 75% (just shy of doubled).
Scrape your dough onto a floured surface and shape into ball (instructions below). Cover and rest for 30 minutes.
Turn dough over and shape one additional time following instructions from step 7.
Move dough, seam side up into a well floured shaping basket. Cover basket with a plastic bag and place in the refrigerator for up to 36 hours.
When ready to bake, preheat Dutch Oven in 500 F degree oven for 30 minutes.
Remove olive rosemary sourdough from the refrigerator and turn out onto a piece of parchment paper or silicone baking mat. Use razor blade, bread lame, or sharp knife to score bread to your preference.
Remove Dutch Oven from oven and reduce temperature to 450 F degrees. Place dough into Dutch oven with the lid on and bake in oven for 20 minutes. After 20 minutes, remove the lid and continue to bake for an additional 20 minutes until the bread has a nicely browned crust.
Remove from Dutch Oven and cool for 1 hour before serving.