1. Preheat oven to 425 degrees F. Coat a baking sheet with cooking spray.
2. Combine buttermilk and oil. Whisk whole-wheat flour, all-purpose flour, sugar, baking powder, baking soda and salt in a large bowl. Using your fingertips or 2 knives, cut butter into the dry ingredients until crumbly. Make a well in the center and gradually pour in the buttermilk mixture, stirring with a fork until just combined.
3. Transfer the dough to a floured surface and sprinkle with a little flour. Lightly knead the dough 8 times, then pat or roll out to an even 3/4-inch thickness. Cut into 2-inch rounds and transfer to the prepared baking sheet. Gather any scraps of dough and cut more rounds. Brush the tops with milk.
4. Bake the biscuits for 12 to 16 minutes, or until golden brown. Transfer to a wire rack and let cool slightly before serving.

Yield: 12 servings