Combine first 5 ingredients in a bowl; set aside.
Preheat oven to 425°.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, 3 tablespoons sugar, and cinnamon in a bowl; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Add buttermilk, stirring just until dry ingredients are moist.
Turn dough out onto a heavily floured surface; knead lightly 5 times. Roll dough to 1/2-inch thickness; cut with a 2 3/4-inch biscuit cutter. Place shortcakes on a baking sheet coated with cooking spray. Sprinkle evenly with 2 teaspoons sugar.
Bake at 425° for 12 minutes or until golden. Remove shortcakes from baking sheet, and cool on a wire rack.
Place thawed strawberries in a blender or food processor. Process 20 seconds. Strain puree through a sieve into a bowl; discard solids. Stir strawberry puree into berry mixture.
Cut shortcakes in half. Spoon 1/4 cup fruit mixture over bottom of each shortcake. Place top of shortcakes over fruit mixture; spoon 1/4 cup fruit mixture over tops. Dollop 1 tablespoon whipped topping onto each shortcake. Serve immediately.