To prepare strawberries, combine strawberries and 1/4 cup sugar; cover and chill 1 hour.
Preheat oven to 400°.
To prepare shortcake, lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 5 ingredients (flour through baking soda) in a large bowl, stirring with a whisk. Cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Combine buttermilk and vanilla; add to flour mixture, stirring just until moist (dough will be sticky).
Turn dough out onto a lightly floured surface; knead lightly 4 times with floured hands. Pat dough into an 8-inch circle on a baking sheet coated with cooking spray. Brush top with egg white; sprinkle with 1 1/2 teaspoons sugar.
Bake at 400° for 15 minutes or until a wooden pick inserted in center comes out clean. Cool 10 minutes on a wire rack. Carefully split shortcake in half horizontally using a serrated knife; cool layers separately on wire racks.
Place bottom half of shortcake, cut side up, on a serving plate. Drain strawberries, reserving juice; drizzle juice over bottom half of shortcake. Spread 2 cups whipped topping over shortcake layer; arrange strawberries over whipped topping. Top with remaining shortcake layer, cut side down. Garnish with whipped topping and whole strawberry, if desired.