Prepare the Biga:

1. Combine Ingredients: In a mixing bowl, combine the bread flour, water, and a pinch of instant yeast. Stir with a wooden spoon or Danish dough whisk until well blended.
2. First Fermentation: Scrape down the sides of the bowl, cover with plastic wrap, and let it rest at room temperature (about 75°F) for 14 to 16 hours.

Make the Final Dough:

1. Mix Dry Ingredients: In the bowl of a stand mixer, combine the bread flour, whole wheat flour, and a pinch of yeast.
2. Integrate Biga and Liquids: Add water, milk, and all of the biga. Using the dough hook, mix on low speed until everything is blended.
3. Develop Gluten: Add salt and mix on low speed for 5 minutes. Increase the speed to medium and mix for an additional 7 minutes, or until the dough is smooth and elastic.
4. Add Flavorings: On low speed, gradually mix in the olive oil and chopped rosemary until evenly distributed.
5. Bulk Fermentation: Lightly oil a large bowl. Transfer the dough to the bowl, cover with plastic wrap, and let it ferment at room temperature for about 7 hours.
6. Divide and Shape: Turn the dough out onto a lightly floured surface. Divide into four equal pieces (450 grams each). Shape each piece into a tight round.
7. Bench Rest: Cover the dough rounds with plastic wrap and let them rest for 15 minutes.
8. Final Shaping: Degas the dough gently and shape into final rounds.
9. Proof: Arrange the loaves on a parchment-lined baking sheet. Cover and let proof for 1 hour.
10. Preheat Oven: About an hour before baking, place a baking stone and a steam pan in the oven. Preheat to 450°F (232°C).
11. Score and Bake: Uncover the dough. Score the top of each loaf in a star pattern. Add ice to the steam pan. Bake for 30 minutes, or until golden brown and hollow sounding when tapped.
12. Cool: Transfer loaves to a wire rack to cool completely.