1. In a large mixing bowl, combine yeast and the warm water; let stand until yeast is dissolved and bubbles form on the surface, about 5 minutes.

2. Heat buttermilk in a small saucepan over medium heat until it is warm to the touch, and add to yeast mixture. Using a wooden spoon, gradually stir 3 cups flour into yeast mixture until it is combined but mixture is still soupy. Cover with a kitchen towel; let stand in a warm place 8 to 12 hours.

3. Add 1 cup flour to mixture, and let stand, covered, 12 hours more.

4. Add 5 cups flour and the salt, and stir until mixture just comes together. Turn out onto a well-floured work surface, and knead 5 minutes, adding more flour as necessary; the dough will be very sticky. Place in a lightly oiled bowl, and cover with plastic wrap. Let rise until it is doubled, about 2 hours.

5. Preheat oven to 350 degrees. Line a baking sheet with parchment paper, and lightly dust parchment with flour. Using floured hands, punch down dough and turn out onto a lightly floured work surface. Form into a large round loaf. Place on prepared baking sheet, and cover with a damp kitchen towel; let rise until dough is doubled and beginning to crack on the surface, 45 to 60 minutes.

6. Bake until loaf is nicely golden and makes a hollow sound when tapped on the bottom, about 60 minutes. Transfer to a wire rack to cool before serving.