In a medium mixing bowl, sift together first five ingredients. Using a food processor or pastry cutter, cut butter into dry ingredients until butter is in pea-sized pieces; using a fork, stir buttermilk into dry ingredients just until dough is uniformly moist (there will be lumps). Move dough to a large sheet of waxed paper; use a second sheet of wax paper (not your hands) to fold dough in half a few times. Pat to an even 1" thickness, taking care not overwork the dough. Using a 2 1/2" round cutter dipped in flour, cut straight down into dough to form biscuits (DO NOT twist cutter, and remember to dip the cutter in flour each time). If necessary, gather scraps of dough and quickly re-knead, roll and cut remaining dough. Bake in a preheated 450° oven on a baking sheet lined with parchment paper until light brown on top (8-10 min.).