1. Preheat oven to 400°.
2. Weigh or lightly spoon flours and potato starch into dry measuring cups; level with a knife. Combine flours, potato starch, oats, and next 7 ingredients (through nutmeg) in a large bowl, stirring with a whisk; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Stir in apple and baking chips. Add buttermilk and applesauce; stir just until moist.
3. Turn dough out onto a surface lightly dusted with white rice flour. Pat dough into an 8-inch circle; cut into 14 wedges. Place wedges on a baking sheet lined with parchment paper. Brush egg white over surface of dough; sprinkle with turbinado sugar. Bake at 400° for 14 minutes or until golden brown. Remove scones from baking sheet to a wire rack. Serve warm.