1. Place strawberries, 1/4 cup powdered sugar, and juice in a small bowl; toss.
2. Preheat oven to 425°.
3. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 5 ingredients (through salt) in a large bowl, stirring well with a whisk. Cut in butter with a pastry blender or two knives until mixture resembles coarse meal. Add buttermilk, stirring just until moist.
4. Turn dough out onto a lightly floured surface; knead one or two times until well blended. Pat dough into a 6 x 4–inch rectangle. Cut dough into 6 (2-inch) squares; sprinkle evenly with turbinado sugar. Place squares 1 inch apart on a baking sheet coated with cooking spray. Bake at 425° for 13 minutes; cool on rack.
5. Place whipping cream in a bowl; beat with a mixer at high speed until soft peaks form. Add remaining 2 teaspoons powdered sugar. Continue beating until stiff peaks form. Split shortcakes in half crosswise. Place 1 bottom half of cake on each of 6 plates; top each serving with 1/2 cup strawberry mixture. Spoon 1 1/2 tablespoons whipped cream over each serving. Place 1 top half of cake over each serving.