Levain:

1. In a medium bowl, whisk together the flours. Make a well in the center. Pour in the starter and mix with the water to break it up.
2. Work the starter/water mixture into the flour just until no dry bits of flour remain.
3. Cover, and let rest 6-8 hours in warm room temperature. If the ambient temperature in your kitchen is cooler, you may need to let it rest longer, 10-16 hours.
4. At this point, the levain may be used in the final dough or placed in the refrigerator for up to 3 days.

Final Dough:

1. Pour 500 grams of water and the olive oil in the bowl with the levain. Let rest while you are prepping the other ingredients. Mix to dissolve levain.
2. In a large bowl, whisk together the flours and rosemary, if using. Add the levain mixture to the dry ingredients and mix thoroughly. Let rest 20-30 minutes.
3. Sprinkle the salt over the dough and dissolve with 15-25 grams of water. If the dough begins to tear, add more water as needed while incorporating the salt into the dough.
4. Cover and let rest in a warm place for 2-3 hours. Stretch and fold the dough after 30 minutes and again after 1 hour for a total of 2 stretch and folds. Let rest for remaining 1-2 hours.
5. Turn the dough back out onto a floured work surface and deflate the dough. Divide into 3 equal pieces (650-665 grams each) for medium loaves. Total weight of dough should be between 1950-2000 grams, depending on flour used and how much water you incorporate.
6. Gather up the edges and preshape the dough into a ball. Flip the ball and place it seam side down on the work surface. Push the dough against the work surface in a circular motion to tighten the top. Pull the dough toward you to elongate the dough into an oval (batard) or round (boule) shape.
7. Place in rice flour-dusted and lined oval or round banneton baskets. Let proof for 2-3 hours, longer if the ambient temperature in your kitchen is cooler.
8. After the final proof on the counter, the loaves can be baked immediately or placed in the refrigerator overnight for a cold ferment.
9. Preheat oven to 450 degrees F. with a baking stone on the middle rack and a steam pan on the lowest shelf. I use a small cast iron skillet as my steam pan.
10. Once the oven is sufficiently preheated, gently flip the loaves onto parchment paper. Brush off the excess rice flour, if desired, and dust with all-purpose flour to achieve a nice contrast when baked.
11. Score the loaves in the pattern of your choice, then slide the parchment with the loaves onto the preheated baking stone. Immediately add 1 cup of ice cubes to the preheated steam pan and shut the oven door.
12. Bake for 30-35 minutes. Check after 15-20 minutes and rotate the loaves for even baking. Then continue baking until nicely browned. The loaves should sound hollow when thumped on the bottom.
13. Transfer loaves to a cooling rack and cool before serving.