Preheat oven to 450°.
Lightly spoon the flour into dry measuring cups, and level with a knife. Combine the flour and the next 5 ingredients (flour through baking soda) in a bowl, and cut in the butter with a pastry blender or 2 knives until mixture resembles coarse meal. Add the buttermilk, and stir just until moist.
Turn dough out onto a lightly floured surface, and knead lightly 5 or 6 times. Roll dough to a 1/2-inch thickness, and cut with a 2 1/2-inch biscuit cutter into 8 shortcakes. Place the shortcakes on a baking sheet coated with cooking spray, and sprinkle with turbinado sugar. Bake at 450° for 10 minutes or until golden. Remove shortcakes from baking sheet; cool on a wire rack.
Note: Place the remaining shortcakes in an airtight container, and freeze for up to 2 weeks. Thaw at room temperature.