Heat oven to 400°F. Line a baking sheet with parchment paper or a silicone baking- sheet liner.Advertisement
Combine flour, sugar, baking powder, baking soda and salt in large bowl. Add butter; mix with pastry blender until mixture resembles coarse crumbs. Gently stir vinegar-milk mixture into dough, along with blueberries, orange peel and egg just until combined.
Using a standard ice-cream scoop (about 1/2 cup), drop heaping scoopfuls of dough onto prepared sheet, about 2 inches apart. Brush with egg white; sprinkle with sugar.
Bake at 400°F for 12 to 15 minutes or until golden brown. Remove to wire rack to cool slightly. Serve warm or at room temperature with flavored preserves, if desired.