Preheat oven to 350°.
Lightly spoon flours into a dry measuring cup; level with a knife. Combine whole wheat flour and next 6 ingredients (whole wheat flour through salt) in a large bowl; cut in butter with a pastry blender or 2 knives until the mixture resembles coarse meal.
Make a well in center of flour mixture; add buttermilk. Stir just until moist.
Turn dough out onto a lightly floured surface; knead lightly 5 or 6 times. Pat dough into an 8-inch circle on a baking sheet lightly coated with cooking spray. Using a sharp knife, score dough by making 2 lengthwise cuts 1/4 inch deep across the top of the loaf to form an X. Bake at 350° for 35 minutes or until a wooden pick inserted in center comes out clean. Cool on a wire rack. Cut into 12 wedges.