For the preferment:
1 cup water
1 cup bread flour
½ tsp. instant yeast
For the dough:
All of the preferment
5 cups bread flour
½ cup nonfat dry milk
1 tbsp. brown sugar or granulated sugar
1 tbsp. salt
2 tsp. instant yeast
1 tbsp. olive oil
2 cups water, at room temperature
To make the preferment, combine the water, flour and yeast in a medium bowl. Mix well to blend, cover with plastic wrap, and let sit at room temperature at least 4 hours and up to 16 hours.
When you are ready to make the dough, in the bowl of a stand mixer fitted with the paddle attachment, combine the preferment, 4 cups of the flour, dry milk, sugar, salt, yeast, olive oil and water. Mix on low speed until a sticky dough has formed. Switch to the dough hook and add the remaining flour ¼ cup at a time. Continue kneading on low speed until the flour has been incorporated (you may need to add even more than 5 cups) and you have a dough that is smooth and elastic, and no longer sticky. The total kneading time should be about 10 minutes.
Transfer the dough to a well greased bowl, turning once to coat, and cover with plastic wrap. Allow to rise at room temperature until approximately doubled in size, about 2 hours. Punch down the dough, cover once more, and let rise again for 30 minutes.
Turn the dough out onto a lightly floured work surface. Knead the dough once or twice and divide into two equal portions. Cover the two pieces of dough with a damp towel and allow to relax for 20 minutes.
Shape the two portions of dough into the desired final shape and transfer to a baking sheet lined with parchment or a silicone baking mat (I used a baguette pan). Cover again with a damp kitchen towel and let rise until approximately doubled in bulk, about 1 hour.
Preheat the oven to 425˚ F. Just before placing the loaves in the oven, brush or spray them lightly with water. Place in the oven and bake for 20 minutes before rotating them. Bake another 20-30 minutes, or until the internal temperature reaches 200˚ F. Remove from the oven, transfer to a wire cooling rack and let cool at least 30 minutes before slicing and serving.