Adjust oven rack to upper-middle position and heat oven to 425 degrees. Grease 9" cake pan. Combine flours, baking powder, baking soda, and salt in large bowl. Rub butter and shortening into flour mixture until it resembles coarse meal (I use a pastry blender). Stir in buttermilk JUST until combined.
Use greased 1/2 c measuring cup or large spring loaded ice cream scoop to transfer 6 heaping portions of dough into prepared pan, placing 5 around the perimeter and one in the center.
Bake until puffed and golden brown, 20-25 minute Cool in pan 10 min then transfer to wire rack. Serve.