1. Preheat oven to 400°. Combine first 5 ingredients; cut in butter with pastry blender until mixture resembles a coarse meal.
2. Whisk together the buttermilk, egg, and vanilla. Add to dry ingredients with cranberries; stir just until moist.
3. On lightly floured surface, knead dough with floured hands 5 or 6 times; pat into 7-inch round. Cut into 6 wedges; transfer wedges to parchment-lined baking sheet.
4. Brush tops with egg white, and sprinkle with coarse sugar. Bake 15 minutes or until golden. Let cool on wire rack 10 minutes before serving.