Preheat oven to 450°. Sift dry ingredients into large bowl. Add buttermilk slowly to make soft dough. Hint: Work quickly because buttermilk and soda will begin to react quickly. Knead dough lightly too much handling will toughen it, while too little means dough may not rise properly. Form into round loaf, about 2 inches thick. Place on lightly floured baking sheet; cut cross in top with floured knife. Bake at 450° 30 to 45 minutes. When baked, loaf will sound hollow when rapped on bottom with your knuckles. Wrap in cloth to stop crust from becoming too hard.