Preheat oven to 400°.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, 3 tablespoons sugar, 1 teaspoon cinnamon, and next 3 ingredients in a large bowl. Cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Stir in apple.
Combine buttermilk and egg yolk; add to flour mixture, stirring just until moist.
Turn dough out onto a lightly floured surface; knead lightly 4 to 5 times with floured hands. Pat dough into a 7-inch circle on a baking sheet coated with cooking spray. Cut dough into 10 wedges; place wedges 1 inch apart on baking sheet.
Beat egg white with a fork until frothy; brush over surface of dough. Combine remaining 1 tablespoon sugar and 1/2 teaspoon cinnamon; sprinkle evenly over dough. Bake at 400° for 12 to 14 minutes or until lightly golden. Serve warm.