1. The day before making the bread, make the soaker by mixing the cornmeal and water in a small bowl. Cover with plastic wrap and let sit overnight at room temperature.
2. The next day, to make the dough, stir together 2 cups of the flour, the yeast, soaker, and water in a mixing bowl (or in the bowl of an electric mixer). Cover the bowl with a towel or plastic wrap and ferment for 1 hour, or until the sponge begins to bubble.
3. Add the remaining 2½ cups of flour, the salt, molasses, and butter and stir (or mix on low speed with the paddle attachment) until the ingredients form a ball. Add water if necessary to make a soft, slightly sticky mass.
4. Sprinkle flour on the counter, transfer the dough to the counter, and begin kneading (or mix on medium speed with the dough hook), sprinkling in more flour as needed to make a tacky, but not sticky, dough. The dough should be firm but supple and pliable and definitely not sticky. It will take about 10 minutes of kneading to accomplish this (or 6 to 8 minutes in the electric mixer). The dough should pass the windowpane test and register 77° to 81° F.
5. Lightly oil a bowl and transfer the dough to the bowl, rolling it around to coat it with the oil. Cover the bowl with plastic wrap and ferment the dough at room temperature for about 90 minutes, or until it doubles in size.
6. Remove the dough from the bowl and divide it into 2 equal pieces of 24 ounces, or 3 pieces of about 16 ounces. Shape the dough into loaves, and place them into bread pans that have been lightly oiled or misted with spray oil. Mist the tops of the loaves with spray oil and loosely cover the tops with plastic wrap.
7. Proof at room temperature for 60 to 90 minutes, or until the loaves crest fully above the tops of the pans.
8. Preheat the oven to 350°F with the oven rack on the middle shelf. Place the pans on a sheet pan and remove the plastic wrap. Mist the tops with a spray of water and dust with cornmeal.
9. Place the sheet pan in the oven and bake for 20 minutes. Rotate the sheet pan for even baking and continue to bake for 20 to 30 minutes, or until the loaves are golden brown, including along the sides and bottom, and register at least 185° to 190°F in the center. They should make a hollow sound when thumped on the bottom.
10. When the loaves are done, remove them immediately from the pans and cool on a rack for at least 1 hour before slicing or serving.