In the bowl of a stand mixer, combine flour and salt. Mix together. (Don’t skip this step.)
Add rosemary leaves and yeast.
Add water, olive oil and sourdough starter.
Use a flat beater to combine ingredients. Stir only until mixed.
Cover bowl and let rest for 10 minutes.
Use dough hook to mix until dough is smooth, about 5 or 6 minutes.
Place dough in large lidded container that has been sprayed with cooking spray and snap on lid.
Every 20 minutes for the first hour of rising time (at 20, 40, and 60 minutes), turn dough out onto a heavily flour surface and fold the top third of the dough in on itself. Fold the top third up. (like a letter) Repeat with short sides.
Place seam side down back into prepared container.
After this has been done three times, at 20, 40, and 60 minutes, leave the dough alone and let it continue to rise for 5 more hours.
Turn the dough out onto floured surface and divide it in half using a bench knife.
Round dough and place each piece in a floured banneton, either lined or unlined. Cover.
Allow to rise for an additional 3 hours. (If it’s getting late, you can refrigerate at this point. Depending on how tired I am is how I decide which to do.)
Turn shaped dough out onto a piece of parchment.
Score the top.
Use a peel or the back of a sheet pan to place dough on preheated stone in 450 degree oven and bake for 20 to 25 minutes, until desired degree of doneness is reached. (If possible, fill the oven with steam while baking. You will be rewarded with a shinier, crisper crust.) After removing from oven, place bread on cooling racks.
To fill your oven with steam, place a cast iron pan on the rack under your stone and preheat with your stone. When you put your bread in the oven, throw a handful (or cupful) of ice into the cast iron pan. (Be careful of the steam!) Alternatively, you can spritz the oven with water (in a spray bottle) when you put your bread in.