Biga:

1. In a medium bowl, whisk together the flour and yeast. Pour in the water and mix with a dough whisk or wooden spoon just until the biga ingredients are combined. The dough will be sticky.
2. Shape into a ball, cover, and let rest for 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.

Final Dough:

1. Pour 250 grams of water and the olive oil in the bowl with the biga. Let rest while you are prepping the other ingredients. Mix to dissolve biga.
2. In a large bowl, whisk together the flours, yeast, and rosemary, if using. Add the water/biga mixture to the dry ingredients and mix thoroughly. Let rest 20-30 minutes.
3. Sprinkle the salt over the dough and dissolve with 10-25 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 1-2 hours, until very puffy, more than doubled. 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 30 minutes to 1 hour.
5. Turn the dough back out onto a floured work surface and deflate the dough. Divide into 2 equal pieces for medium loaves. Total weight of dough should be between 960-1000 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 shape). Place in rice flour-dusted and lined oval banneton baskets. Let proof for 30-45 minutes while the oven is preheating.
7. Preheat the 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.
8. Gently flip the proofed 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. Score the loaves, then slide the parchment with the loaves onto the preheated baking stone. Immediately add a cup of ice cubes to the preheated steam pan and shut the oven door.
9. 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.
10. Transfer loaves to a cooling rack and cool before serving.