Step 1Heat the oven to 425 degrees. Line a rimmed baking sheet with parchment.Step 2In a bowl, whisk together flours, baking powder, sugar and salt. Using a pastry cutter or fork, quickly cut in 8 tablespoons butter until it forms pea-size crumbs and is uniformly mixed it (for flaky biscuits you want the butter to remain cold). Make a well in the center of the flour mixture and pour in buttermilk. Stir together until it just forms a moist, slightly tacky dough.Step 3Turn dough out onto a lightly floured surface. Knead 2 or 3 times, then pat out into a 3/4-inch-thick round. Using a 2-inch round cutter, cut the biscuits. Twisting the cutter prevents proper rising; to prevent sticking, dip the cutter lightly in flour between biscuits. Do not re-roll the scraps, but pat them together and cut into rounds. Transfer biscuits to the baking sheet.Step 4Melt remaining 1 tablespoon butter. Brush butter lightly over the tops of biscuits. Bake until puffed and golden, about 15 to 20 minutes. Cool 5 minutes before serving.