Heat oven to 350F. Grease a large cast-iron skillet or baking sheet. In a large bowl, mix 4 C. flour with the baking powder, baking soda, and salt. Add butter and rub it into the flour by scooping up handfuls of the mixture and rubbing it between the palms of your hands until pieces of butter are no longer visible. Add buttermilk to a bowl and stir with a wooden spoon until mixture forms a dough. Sprinkle about 1/4 cup of remaining flour on a board. Turn out dough and knead lightly for about 1 minute, working in the flour from the board and forming dough into a smooth, round loaf about 8 inches in diameter. Put loaf, smooth side up, in prepared pan and cut a deep cross in it, slicing three-fourths of the way through the dough. Bake 55-60 minutes, or until loaf sounds hollow when tapped on the bottom. Cool on a wire rack. Contributed by: Andrew Balinsky (balinsky@cs.umd.edu)