Preheat oven to 400 degrees. Add all of the dry ingredients in a large bowl and mix very well, being very careful to break up any lumps of brown sugar. Pour all of the buttermilk into the bowl at once and stir, using a wooden spoon, just until a soft dough is formed. Do not try to make it smooth at this point. Pour the contents of the bowl out onto a plastic counter and knead for a minute or so until everything comes together. Divide thedough into 2 portions and shape each into a round loaf, pressing the top down a bit to just barely flatten it. Place the loaves on a large ungreased baking sheet. Sprinkle some additional flour on top of each loaf and, using a sharp paring knife, make the sign of the Cross in slashes on the top of each. Bake for about 45 minutes or until brown and crunchy. Cool on racks.