In a standup mixer fitted with the dough hook, combine the flour, starter, salt, and rosemary, and mix on low until ingredients are moistened then increase to medium-high and knead dough until it no longer sticks to the bowl.
Grease a large bowl with olive oil and place dough inside, turning dough over to coat with the oil. Cover with plastic and set in a warm, draft-free place until doubled in size, about 1 hour.
Remove plastic, punch dough down, and dump onto a lightly-floured surface. Knead a few times then shape into a ball.
Place on a baking peel sprinkled with cornmeal, seam-side down. Cover with a damp kitchen towel and let rise until doubled in size, about 1 hour.
Preheat a baking stone on the bottom rack of an oven at 400 degrees F.
With a sharp knife, slash a large X on the top of the dough.
Transfer to the baking stone and bake for 60 minutes or until bread sounds hollow when tapped on the bottom and is lightly browned on top, about 1 hour.
Using the peel, remove bread from the oven and let cool on a wire rack for 30 to 40 minutes before slicing and serving warm.
Once bread is completely cool, store it in an airtight container for up to 4 days.