Blueberry Blackberry Shortcakes

Preheat oven to 400 degrees.
To prepare shortcakes, lightly spoon flour into dry measuring cups; level with a knife.
Combine flour and next 5 ingredients (through salt) in a large bowl, stirring with a whisk.
Cut in chilled butter with a pstry blender or 2 knives until the mixture resembeles coarse meal.
Add buttermilk, stir just until moist.
Turn dough out onto a lightly floured surface; knead lightly 4 times.
Pat dough to a 1/2 inch thickness; cut with a 3 inch biscuit cutter to form 8 dough rounds.
Place dough rounds 2 inches apart on a baking sheet coated with cooking spray.
Combine water and egg white, stirring with a whist; brush over dough rounds.
Sprinkle evenly with 2 teaspoons sugar.
Bake at 400 degrees for 13 minutes, or until golden.
Remove from oven, and cool on a wire rack.
To prepare filling, combine 1 cup blueberries, 1/2 cup sugar, juice and cornstarch in a small saucepan.
Bring to a boil; reduce heat, and simmer 5 minutes or until slightly thick.
Place in a large bowl; add remaining 2 cups blueberries and blackberries, stirring to coat.
Cover and chill.
Using a serrated knife, cut each shortcake in half horizontally; spoon 1/2 cup blueberry mixture over bottom half of each shortcake.
Top each serving with 2 tbsp whipped cream and top half of shortcake.