In a 4-quart (16 cups) bowl, combine flour, yeast, and salt.
Pour in water and buttermilk, and mix until ingredients are moist.
Reach over the sides of the bowl and fold the dough towards the center 40 times.
The dough will be sticky.
Cover the bowl with plastic wrap and let the dough rise at room temperature (72 F/22 C), away from drafts, for 2 hours, until it almost reaches the top of the bowl and has the texture of a sponge.

After 2 hours, bake the dough the same day or store it in the refrigerator under plastic wrap. It will keep for almost 3 days.

Transfer the dough to a floured surface and divide it into 2 equal parts.
Transfer one half to a floured surface and sprinkle it with a little flour.
Shape a 9″ (23 cm) cylinder, handling the dough as little as possible.
Smooth it out with your hands so that its surface is soft but not sticky.
Pinch any seams, if necessary.
Do the same with the second dough quantity.

Place each dough cylinder in the floured loaf pans.
Cover with a dish towel and let rest at room temperature for 40 minutes.

Preheat oven to 425 F (220 C), 30 minutes before baking the dough.
Place another rack under the middle rack and put a broiler pan filled with water on it.

Bake the loaves and just before closing the oven door, spray the walls with cold water to give them a “steam boost”.
Bake for 30 minutes.
Remove from oven, unmold the loaves, and let them cool on a cooling rack.