How to Make It
To prepare pastry, lightly spoon flour into dry measuring cups, and level with a knife. Combine flour and next 3 ingredients (through salt) in a food processor; pulse two times. Add butter to flour mixture; pulse 4 to 5 times or until mixture resembles coarse meal. With processor on, slowly add buttermilk through food chute; process just until dough forms a ball. Gently press dough into a 4-inch circle on plastic wrap; cover. Chill 30 minutes.
Preheat oven to 350°.
Unwrap and place dough on a sheet of parchment paper. Roll dough into a 15-inch circle. Place dough and parchment on a baking sheet.
To prepare filling, combine berries and next 3 ingredients (through juice) in a medium bowl; toss gently to coat. Arrange berry mixture in center of dough, leaving a 2-inch border. Fold edges of dough toward center, pressing gently to seal (dough will only partially cover berry mixture).
Combine fat-free milk and egg white in a small bowl, stirring well with a whisk. Brush dough with milk mixture; sprinkle turbinado sugar evenly over dough. Bake at 350° for 1 hour or until pastry is golden brown. Let stand 30 minutes; cut into wedges.