In the bowl of an stand mixer (or a large bowl, about 6 qt capacity), mix together the water, buttermilk, yeast, salt and sugar. Add the flour and mix using the paddle attachment (or mix by hand with a wooden spoon). Do not knead the dough.
Lightly cover the bowl and let it rest at room temperature for 2 hours, or until the dough doubles in size, then collapses.
At this point, the dough can be used immediately, or it can be stored in the refrigerator in a covered container and used within 5 days. The dough can also be stored in the freezer for up to 3 weeks.
When you are ready to bake, cut off your desired amount from the dough. I baked free form loaves from portions about the size of a grapefruit on a baking stone. Dust the portion of dough with flour and very lightly knead and shape it into an elongated ball. Lightly cover with a kitchen towel or plastic wrap and let it rest for 90 minutes.
Preheat the oven to 350 degrees F. Place the rack in the center of the oven with the baking stone, if using.
If baking on a baking stone, lightly dust the bottom of the loaf with cornmeal. Otherwise, place on a parchment lined baking tray. Lightly brush the top of the loaf with melted butter. Bake for about 45 minutes, or until the bread is golden brown. Brush the top of the bread with a little more melted butter upon removing from the oven. Take the bread out of the pan and cool before slicing.